Superconductors, high critical current

The most distinguishing features of superconductive materials are the sudden and complete disappearance of electrical resistance below T, the high critical current density J ), which allows superconductors to conduct with no power loss and the high critical magnetic fields (H 2) in which superconductivity can exist. The relationship among these features is shown in Figure 3,... 

Although deposition conditions for the preparation of YBa2Cu307-5 films are often optimized to produce c-axis-oriented films that exhibit high critical currents, polycrystalline films appear to be better suited for the fabrication of sensitive conductive polymer/superconductor structures. These superconductor thin films are more textured and have lower critical currents than the smooth films, which are prepared with what would normally be considered more optimized deposition conditions. The weak link characteristics of these thin films are also enhanced by depositing the superconductor onto cleaved MgO substrates. These substrates possess natural step edges and can be exploited to further disrupt the connection between selected superconductor grains. 

The current transfer problem that had been identified with low temperature superconducting composites deserves additional mention for the high temperature superconductors, that in the bulk material are frequently not fully dense. Making the electrical connection in such a manner as to obtain uniform current distribution throughout the cross section of the material is difficult. The method described by Jin, et al. (24) with embedded wires or particles may provide for a significant improvement but the present techniques used to determine the critical current by a surface contact on the ceramic sample are subject to this problem. A discussion for the multifilamentary wire of NbsSn is provided by Goodrich and Fickett (30) and this discussion is likely to be similar to the high temperature materials that are not fully dense. 

McGinnis, W., Jones, T., Jacobs, E., Boss, R. and Schindler, J., Critical Current Densities for the High Temperature Ceramic Superconductors Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O. 1988 Applied Superconductivity Conference, San Francisco, CA (1988). 

Melikhov, E. and Gershanov, Y., Percolation Model of Ceramic High-Tc Superconductors. Critical Current and Current Voltage Characteristic, Physica Cl57 431 (1989). 

Aponte, J., Abache, H., Sa-Neto, A. and Octavio, M., Temperature Dependence of the Critical Current in High-Tc Superconductors, Phys. Rev. B39 2233 (1989). 

The high critical temperature superconductors show a strong anisotropy in different properties critical current density [1], resistivity [2, 3] and the upper critical field [2],... 

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