Effect of Nb doping on properties of Y-Ba-Cu ceramics

The properties of Nb-doped YBa2Cu3Oy ceramics obtained by thermolysis of the oxide or nitrate (Y, Ba, Cu) solution in ammonium nitrate melt were studied. For the composition YBa2Cu3-xNb0.05O6.6, Tc = 92 K and the transport critical current Jc = 1000-4000 A cm-2 were obtained. The magnetic flux profile was studied by a magneto-optic method at B = 290 G. Domains of size 200-600 mu m were found with magnetic critical current Jcm = 2 * 104 A cm-2 at 77 K and 105 A cm-2 at 11 K.