Transport critical current of filamentary Zr-doped Gd-Ba-Cu-O superconductors in high magnetic fields

Filamentary Gd-Ba-Cu-O superconductors doped with nominal Zr concentrations between 0 and 0.5 at% relative to Gd123 were prepared by a solution spinning method. Samples were partially melted in flowing 20% O-2 + Ar atmosphere gas at various partial melting temperatures and oxygenated in pure oxygen gas. High J(c) value of 2 x 10(4) A/cm(2) at 77 K and 0 T were obtained for the Gd123 + 0.1 at% Zr sample optimally processed. In the case of doping levels less than 0.5 at%, T-c values, which were about 92 K with sharp transitions, were hardly influenced by Zr concentration. From transport critical current measurements in magnetic fields, the J(c) value of the pure Gd123 filament sharply decreased with increasing applied field. Gd123 with 0.5 at% Zr doping processed under optimum conditions showed little deterioration of J(c) values in low magnetic fields and J(c) values higher than 10(3) A/cm(2) was maintained up to 14 T. It was also found that J(c)s in high magnetic field and the irreversibility field were improved by a small amount of Zr doping.