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.