In article ,
Martin Brown wrote:

Most of the high Tc cermic superconductors are superconducting in LN2
but the problem is they are brittle ceramics and hard to make into
coils, and even worse when you try to make them carry large currents the
resulting magnetic fields take it out of the superconducting state.

All right - I should have added "practical" :-)

Toxicity of barium dust is the main worry in the preparation.
US schools info includes "do not eat" warnings.

Which is, I suppose, why people are given barium meals and enemas
for intestinal X-rays. By the pint :-(

My understanding is that breathing barium dust is bad news, but so
is breathing large quantities of chalk, and that is a beneficial
foodstuff even if eaten in handfuls.


Regards,
Nick Maclaren.