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.

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.

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.

Growth of and Critical Current Density of TL2BA2CACU2O8 Superconducting Single Crystals

1992 ◽  
Vol 275 ◽  
Author(s):  
H. M. Duan ◽  
T. S. Kaplan ◽  
B. Dlugosch ◽  
A. M. Hermann
Keyword(s):  
Critical Current Density ◽  
Single Crystals ◽  
Critical Current ◽  
Liquid Nitrogen ◽  
Current Density ◽  
Liquid Nitrogen Temperature ◽  
Critical Currents ◽  
Different Temperatures

ABSTRACTLarge single crystals of Tl2Ba2CaCu2O8 superconductors were grown by a two step self-flux process. Crystals are plate-like. The in-plane crystal sizes are as large as 5mmX5mm and the thickness range from 0.01mm to 0.8mm. The critical currents were extracted from I-V curves measured at different temperatures. jc was about 2.4×104 A/cm2 at liquid nitrogen temperature.

Insertion versus Growth of Magnetic Nanoparticles in MgB2 Superconducting Composites

2014 ◽  
Vol 941-944 ◽  
pp. 458-461
Author(s):  
Viorel Sandu ◽  
Gheorghe Aldica ◽  
Petre Badica ◽  
Andrei Kuncser ◽  
Yuichiro Hayasaka
Keyword(s):  
Magnetic Nanoparticles ◽  
Critical Current Density ◽  
Critical Current ◽  
Spark Plasma Sintering ◽  
Current Density ◽  
Magnetic Interaction ◽  
Flux Lines ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Organic Precursors

MgB2-based superconducting composites with magnetic nanoparticles were fabricated by spark plasma sintering technique. Two methods have been used to create nanoparticles within MgB2 matrix: i) direct insertion of passivated magnetic nanoparticles; ii) growth of magnetic nanoparticles by thermolysis of polymers or metallo-organic precursors. These composites display an enhanced critical current density due to the additional magnetic pinning generated by the magnetic interaction with the flux lines.

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