Critical current density, temperature

The alloy niobium titanium (NbTi) and the intermetaUic compound of niobium and tin (Nb.3 Sn) are the most technologically advanced LTS materials presently available. Even though NbTi has a lower critical field and critical current density, it is often selected because its metallurgical properties favor convenient wire fabrication. In contrast, Nb.3Sn is a veiy brittle material and requires wire fabrication under very well-defined temperature conditions. 

Critical care analytes, measuring, 24 55 Critical cooling rate, of steel, 23 283 Critical current density, 23 821-823, 825 optimization of, 23 829 in PIT conductors, 23 833-834 temperature and field dependence of, 23 847-848... 

Temperature measurement(s), 24 433-467, 75 469, 77 783-784 of critical current density, 23 847-848 fixed-point thermometer calibration,... 

Fig. 4.10 Critical current density JPS of (100) oriented silicon electrodes for different HF concentrations plotted versus the inverse absolute temperature 1/71 Arrhenius-type behavior, with an activation energy of 0.345 eV, is observed.

Figure II. Schematic anodic polarization curves at a fixed temperature. Determination of either transpassive potential ( ,) or pitting potential ( p and repassivation potential ( ,) at the critical current density (/ ). t rcvis the current density at which the scan is reversed. ...

Film Critical Current Densities Critical current densities of thin films have been reported by several hundreds of papers a few representative but by no means inclusive are noted here in addition to those mentioned above. Desirable attributes of thin films for technology are high transition temperature to zero resistance, high critical current, low substrate temperature during deposition, no high temperature post anneal, and atomically smooth surface without pinholes. A thermal coevaporation of yttrium, barium, and copper in an oxygen atmosphere have been deposited by Berberich (34) on substrates at 650°C with Tc s of 91 K on MgO and 89 K on SrTiOs without post anneal. Although critical currents of 106 A/cm2 were obtained at 4 K, values of 104 A/cm2 were found at 77 K. However,... 

Figure 12b Critical current density vs magnetic field applied normal to the film surface and current direction for a thin film microbridge of Y-Ba-Cu-O at various temperatures. Ref. 31.

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],... 

The nonlinearities in the curves of Fig.3 can be explained by current flowing processes through superconducting areas in the contact region. The behavior of the curves conforms to that of superconducting inclusions in dirty contacts when the system reaches the critical current density and when the temperature increases [15]. 

FIGURE 57 Critical current density of HoNi2B2C as a function of temperature at the same reduced field of H/Hc2 = 0.05 for the two field orientations H c and H a. After Krutzler et al. (2005). 

The strong inverse dependence of critical current density on magnetic field at 77 K is a limitation associated with Bi-2223 tape. This necessitates operation at lower temperatures for certain applications (e.g. electromagnets) when the cable is subjected to strong magnetic fields. This limitation does not arise with the (RE)BCO system and intensive efforts are being made to manufacture suitable tapes. 

High- temperature superconduc- tors Transmission cables, transformers, current limiters, motors and generators Rolling, direct metal oxidation, tape casting Greater energy efficiency, higher critical current density... 

The E-I curve in Fig. 3 was obtained at 25° C. If the temperature of the silicon is varied, the critical current density also changes. The realtion between ic and temperature in 5% HF aqueous solutions is shown in Fig. 4. The critical current... 

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