This plausible direct relation between Bc and Jc is only true
for Type I superconductors,
whereas in Type II superconductors, Jc depends in a complicated way on the interaction between the current and thel ux vortices. New high-rc
superconductors have exceedingly high critical fields, as apparent in Table 8.7, that do
not seem to necessarily translate to high critical current densities. The critical current
density in Type II superconductors depends not only on the temperature and the
applied magnetic field but also on the preparation and hence the microstructure (e.g. ,
polycrystallinity) of the superconductor material . Critical current densities in new
high-rc superconductors vary widely with preparation conditions. For example, in
Y-Ba-Cu-O
,
Jc may be greater than 1 07 A cm-2 in some carefully prepared thini lms
and single crystal s but around 1 03-1 06 A cm-2 in some of the polycrystalline bulk
material (e.g. , sintered bulk samples). In NbsSn, used in superconducting solenoid
magnets, on the other hand, Jc i s close to 1 07 A cm-2 at near 0 K.
This plausible direct relation between Bc and Jc is only truefor Type I superconductors,whereas in Type II superconductors, Jc depends in a complicated way on the interaction between the current and thel ux vortices. New high-rcsuperconductors have exceedingly high critical fields, as apparent in Table 8.7, that donot seem to necessarily translate to high critical current densities. The critical currentdensity in Type II superconductors depends not only on the temperature and theapplied magnetic field but also on the preparation and hence the microstructure (e.g. ,polycrystallinity) of the superconductor material . Critical current densities in newhigh-rc superconductors vary widely with preparation conditions. For example, inY-Ba-Cu-O,Jc may be greater than 1 07 A cm-2 in some carefully prepared thini lmsand single crystal s but around 1 03-1 06 A cm-2 in some of the polycrystalline bulkmaterial (e.g. , sintered bulk samples). In NbsSn, used in superconducting solenoidmagnets, on the other hand, Jc i s close to 1 07 A cm-2 at near 0 K.
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