Critical current density superconductors

Metallic taste, 11 565 Metallic tungsten, 25 374 Metallic Type II superconductors, critical current density value in, 23 822 Metallic vanadates, 25 513 Metalliding, 15 251 Metalliferous oxides deposits of, 17 689-690 in ocean basins, 17 693 Metalliferous sulfide deposits, 17 690-691 Metalliferous sulfides, in ocean basins, 17 693-694... 

The rather low critical current densities expected in bulk samples of these granular superconductor materials (103)(104), and their relatively low magnetic critical fields (50)(78)(105)(106), allied with the relatively low Tc s observed would appear to hinder development of superconducting applications for these materials. Even the critical current of 5 X 105 A/cm2 observed for single crystalline thin films (39) is now considered low for a superconductor at 4.2K. However, when considering the applicability of a material to a task,... 

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). 

In addition to a critical temperature and critical field, all superconductors have a critical current density, Jc, above which they will no longer superconduct. This limitation has important consequences. A logical application of superconductors is as current-carrying media. However, there is a limit, often a low one, to how much current they can carry before losing their superconducting capabilities. The relationship between Jc, He, and Te for a Type II superconductor is shown in Figure 6.32. Notice that the Hc-Tc portion of this plot has already been presented in Figure 6.10 for a Type I superconductor. 

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],... 

Because useful currents carried by a Type I superconductor generate magnetic fields it follows that there are also critical current densities Jc, corresponding to the critical applied magnetic fields. In a Type II superconductor the... 

Considering a specific example (see Question 20), if a cylindrical, circular section superconductor is magnetized along its length the critical current density J flows throughout the volume in circular paths in planes perpendicular to the axis of the cylinder. The interaction of Jc with the penetrated induction 5p, leads to tensile stresses of magnitude 4/ 0-... 

In addition to the critical parameters Tc and Hc, there is also the critical current density jc, above which the superconductor returns to the normal state (see Table 8.5). 

Ren et al. [81] showed that the critical-current density Jc can be enhanced from 7.6 x 103 A/cm2 at 77 K and zero magnetic field to 1.2 x 104 A/cm2 under the same conditions by the addition of 0.1 formula weight of Sn02 to Tl-2223 superconductor. Also, they have suggested that the role of Sn02... 

Further examples of positron study of defects in HTSC are studies carried out to understand the nature of flux-pinning defects that lead to an increase in critical-current density on neutron-irradiated Y 1 2 3. Experiments [59] on positron lifetime and critical-current density measurements on various neutron-irradiated samples of Y 1 2 3 indicate that the critical current density is correlated with the micro-void density, as obtained from the analysis of positron lifetime measurements. Investigation of defects in other HTSC superconductors, such as La-Sr-Ca-Cu-0 [60], Bi-Sr-Ca-Cu-0 [49], and Nd-Ce-Cu-O [52], have also been carried out. 

Superconductivity is the absence of resistance to dc conduction this occurs only below a critical temperature Tc, a critical magnetic field (which is a function of T and current density j), and a critical current density j, which is a function of T and H. For alloys, does not exceed 23 -24 K (by contrast, some of the recently discovered ceramic high-Tc cuprate superconductors, such as HgBa2Ca2Cu30j , have Tc values as high as 140 K and can have comparable y c values), Designers of superconducting solenoid magnets... 

If the current is gradually increased in magnitude, then eventually B will reach the value of the critical field B and the superconductor will go normal. The current density J that is present when the superconductor goes normal is called the critical current density J, Its value is obtained by inserting equation (12) into equation (13) to give... 

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,... 

The prospects for various applications depend, of course, on the materials properties of the superconductor. Many properties are important, including mechanical properties, interfacial interactions and contacts, high frequency loss, and so forth. Here we emphasize as an example the critical current density, which is one of the most vital properties for most applications. 

A/cm2 at 77 K, more than an order of magnitude lower than at 4.2 K. Thus YBaCuO at 77 K has a fundamental disadvantage in zero-field critical current density compared to, say, Nb3Sn at 4.2 K. The same effect impacts the hope for practical room temperature superconductors To maintain reasonable critical current density at 300 K or 27 C, the superconducting transition would have to be closer to 400 K or 127 C ... 

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