Grain boundaries in high-Tc superconductors

1988 ◽  
Vol 46 ◽  
pp. 1008-1009
Author(s):  
M.F. Chisholm
Keyword(s):  
Critical Current Density ◽  
Grain Boundaries ◽  
Critical Current ◽  
Current Density ◽  
Weak Link ◽  
Critical Currents ◽  
Pinning Force ◽  
Conduction Path ◽  
Direct Measurements

One crucial property for most superconductor applications is the materials critical current density. Measurements on single crystals of YBa2Cu3O7, show critical currents to be in excess of 105 A/cm2 at 77K. However, polycrystalline samples show values of 103 A/cm2 or less at 77K. The critical current, unlike other superconductivity properties, is not a property of a specific composition but of a specific sample. Defects, introduced during the material processing, exert a pinning force which makes it possible for Type-II superconductors to carry current without losses. At the same time these defects represent an interruption in the structural and chemical order which has been shown to be necessary for superconductivity in the YBa2Cu3Ox phase, and so they may also act as a weak link in the conduction path. The most direct measurements of the role of individual grain boundaries on the critical current density are those of Chaudhari et al. who examined patterned YBa2Cu3O7 films grown on SrTiO3 substrates.

Microtexture Mapping of Elecrtron Backscattered Diffraction in (Bi,Pb)2Sr2Ca2Cu3O10 Superconductor Tapes

2000 ◽  
Vol 659 ◽  
Author(s):  
Sean Li ◽  
Thiam Teck Tan
Keyword(s):  
Critical Current Density ◽  
Grain Boundaries ◽  
Critical Current ◽  
Current Density ◽  
Crystallographic Orientation ◽  
Weak Link ◽  
Large Angle ◽  
Orientation Distribution ◽  
Weak Links ◽  
Electron Backscattered Diffraction

ABSTRACTGrain boundaries is believed to act as weak-links limiting the critical current density (Jc) of bulk high-Tcsuperconductors. The weak-link problem can be greatly reduced by elimination or minimization of the large-angle grain boundaries. It has been reported that the Jc distribution in the transverse cross-section of (Bi,Pb)2Sr2Ca2Cu3O10+x (Bi2223) superconductor tapes follows a parabolic relationship, with the lowest currents occurring at the center of the tapes. The Jc distribution is proposed to be strongly dependent on the local crystallographic orientation distribution of the Bi2223 oxides. However, the local three dimensional crystallographic orientation distribution of Bi2223 crystals in (Bi,Pb)2Sr2Ca2Cu3O10+×superconductor tapes has not been experimentally determined yet. In this work, Electron Backscattered Diffraction technique was employed to map the crystallographic orientation of the crystals in Bi2223 superconductor tapes. From this, the misorientation of grain boundaries and also their distribution are obtained. Through crystallographic orientation mapping, the relationship of the crystallographic orientation distribution, the boundary misorientation distribution and the fabrication parameters may be understood. This can be used to optimize the fabrication processes thus increasing the critical current density in Bi2223 superconductor tapes.

Y2BaCuO5 addition and its effects on critical currents in large grains of YBa2Cu3O7–δ: A quantitative microstructural study

1996 ◽  
Vol 11 (7) ◽  
pp. 1616-1626 ◽  
Author(s):  
Manoj Chopra ◽  
Siu-Wai Chan ◽  
R. L. Meng ◽  
C. W. Chu
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Flux Pinning ◽  
Crack Opening ◽  
Critical Currents ◽  
Interparticle Spacing ◽  
Pinning Force ◽  
Volume Percent ◽  
Initial Volume

The addition of Y2BaCuO5 (211) particles to large grain melt textured YBa2Cu3O7–δ(Y123) has significantly improved the critical current density (Jc) of this material. Here, a systematic quantitative analysis on the effects of the 211 addition was performed on a microscopic scale with a systematic variation of the initial volume percent of 211. From the correlation between critical current measurements and quantitative microscopy of both (001) and (110) sections, a maximum value of Jc is observed, corresponding to a measured Y123 volume percent of 20% ± 3%. Accounting for the loss of liquid phase for the present processing, the corresponding optimum initial volume of 211 for the highest measured Jc is 40%. Further comparison between the weighted Jc and the true flux pinning force (Fp) also shows a maximum pinning force for an initial 211 addition of 40%. Although the weighted Jc starts to decrease with an initial 211 volume of above 40%, the pinning efficiency at higher magnetic fields (2–4 T) of the superconducting Y123 matrix was actually improved with an ever increasing 211 addition to at least 50%. Though an increasing addition of 211 is effective in producing efficient flux pinning sites in the Y123 matrix, percolation paths in the Y123 matrix become limited for supercurrent. Hence, a measured 211 volume corresponding to 80% 211 is proved to give the best possible critical current density. Furthermore, crack opening and crack spacing of the superficial cracks are found to decrease with an increasing 211 addition and with a decreasing 211 interparticle spacing. The penetration and surface length of each of these superficial cracks are hence reduced, which leads to a better electrical connectivity in the Y123 matrix.

Critical Currents in NbSe2: Evidence for Surface Pinning

1972 ◽  
Vol 50 (22) ◽  
pp. 2840-2841 ◽  
Author(s):  
J. Kopp ◽  
D. J. Huntley ◽  
R. F. Frindt
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Critical Currents ◽  
Flux Flow ◽  
Flux Lines

The variation of critical current density for flux flow with thickness has been measured for crystals of NbSe2 between 10−6 and 0.03 cm thick. The dominant behavior is that [Formula: see text] (thickness)−1 and this is interpreted as evidence for surface pinning predominating over bulk pinning of the flux lines.

Anisotropic critical current density and flux pinning mechanism of Fe1+yTe0.6Se0.4 single crystals

2021 ◽  
Author(s):  
Yongqiang Pan ◽  
Nan Zhou ◽  
Bencheng Lin ◽  
Jinhua Wang ◽  
Zengwei Zhu ◽  
...  
Keyword(s):  
Critical Current Density ◽  
Single Crystals ◽  
Critical Current ◽  
Current Density ◽  
Flux Pinning ◽  
Magnetic Hysteresis ◽  
Magnetic Hysteresis Loop ◽  
Pinning Force ◽  
Magnetization Relaxation ◽  
Pinning Mechanism

Abstract Fe1+yTe0.6Se0.4 has considerable application potential due to its large critical current density (J c) and high upper critical magnetic field (H c2). However, the uncertainty of the anisotropy of J c and the unclear flux-pinning mechanism have limited the application of this material. In this study, the J c in three directions were obtained from magnetic hysteresis loop measurements. A large anisotropy of J c ab /J c c ~ 10 was observed, and the origin of the anisotropy was discussed in details. Flux pinning force densities (F p) were obtained from J c, and a non-scaling behavior was found in the normalized pinning force f p[F p/F p-max] versus the normalized field h[H/H c2]. The peaks of pinning force shift from a high h to a low h with increasing temperature. Based on the vortex dynamics analysis, the peak shift was found to originate from the magnetization relaxation. The J c and F p at critical states free from the magnetic relaxation were regained. According to the Dew-Hughes model, the dominant pinning type in Fe1+yTe0.6Se0.4 clean single crystals was confirmed to be normal point pinning.

scholarly journals Increased flux pinning force and critical current density in MgB2 by nano-La2O3 doping

2020 ◽  
Vol 756 ◽  
pp. 012019
Author(s):  
Danlu Zhang ◽  
Fang Wan ◽  
Michael D. Sumption ◽  
Edward W. Collings ◽  
CJ Thong ◽  
...  
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Flux Pinning ◽  
Pinning Force ◽  
Flux Pinning Force

Grain Boundaries and Critical Current Density of YBa2Cu3O7-y Thick Film Prepared by Liquid Phase Epitaxy

1996 ◽  
pp. 775-778
Author(s):  
Tasuku Kitamura ◽  
Jian-Guo Wen ◽  
Yuh Shiohara ◽  
Naoki Koshizuka ◽  
Izumi Hlrabayashi ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Critical Current Density ◽  
Grain Boundaries ◽  
Thick Film ◽  
Critical Current ◽  
Current Density ◽  
Liquid Phase Epitaxy

PINNING FORCE DENSITY IN YBa2Cu3O7-FILMS AND YBa2Cu3O7/PrBa2Cu3O7-SUPERLATTICES

1993 ◽  
Vol 07 (01n03) ◽  
pp. 135-138
Author(s):  
M. SCHMITT ◽  
T. KLUGE ◽  
C. TOMÉ ROSA ◽  
G. JAKOB ◽  
P. WAGNER ◽  
...  
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Low Temperatures ◽  
Force Density ◽  
Pinning Force ◽  
Axis Of Rotation ◽  
Current Flows ◽  
The Magnetic Field ◽  
Pinning Force Density

The in plane critical current density jc (B, Θ, T) of dc-sputtered YBa 2 Cu 3 O 7-films and YBa 2 Cu 3 O 7/ PrBa 2 Cu 3 O 7-superlattices was measured in dependence of the angle Θ between the magnetic field [Formula: see text] and the [Formula: see text]-axis of the films in two orientations: 1. The current direction is parallel to the axis of rotation (i.e. [Formula: see text] always). 2. The current flows perpendicular to the axis of rotation (i. e. [Formula: see text]). For low temperatures we do not find any difference between the two current orientations, and the critical current density [Formula: see text] behaves like jc (B cos Θ, 0°). For higher temperatures the two cases differ from each other for Θ near to the maxima in jc at 90° and 270° for the YBa 2 Cu 3 O 7-films whereas for YBa 2 Cu 3 O 7/ PrBa 2 Cu 3 O 7-superlattices we hardly find any change for both experimental setups. We compare the behaviour of the experimental results for the two orientations for the YBa 2 Cu 3 O 7-films and YBa 2 Cu 3 O 7/ PrBa 2 Cu 3 O 7-superlattices and discuss the temperature dependence of the intrinsic pinning force density.

INFLUENCE OF GRAIN BOUNDARIES ON THE TRANSPORT CRITICAL CURRENT DENSITY OF HIGH Tc SUPERCONDUCTORS

1991 ◽  
Vol 05 (14n15) ◽  
pp. 993-999 ◽  
Author(s):  
HUIMIN SHAO ◽  
MU LU ◽  
TIANCHANG LU ◽  
XICHUN JIN ◽  
LINJIANG SHEN ◽  
...  
Keyword(s):  
Critical Current Density ◽  
Grain Boundaries ◽  
Critical Current ◽  
Current Density ◽  
Transport Critical Current Density ◽  
High Tc Superconductors ◽  
High Tc ◽  
Preparation Conditions ◽  
Percolation Path ◽  
Superconducting Current

This paper describes our efforts to improve the preparation conditions of YBCO samples and increase their density by doping with Sn, F, or Ag and our analysis of the influence of different grain boundaries on superconducting current. We come to the conclusion that, as the grain boundaries have an insulation layer between them forming Josephson junctions and the metalled grain boundaries form proximity junctions which are kind of weak couplings for superconductors, the current-carrying capacity of samples having such grain boundaries cannot be expected to greatly increase. Only by increasing the density of samples and purifying the grain boundaries can a better percolation path for supercurrent be created, thereby considerably increasing the critical current density.

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