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% O₂ + Ar atmosphere gas at various partial melting temperatures and oxygenated in pure oxygen gas. High J_c value of 2 × 10⁴ A/cm ² at 77 K and 0 T were obtained for the Gd123 + 0.1at%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 10³ A/cm² was maintained up to 14 T. It was also found that J _cs in high magnetic field and the irreversibility field were improved by a small amount of Zr doping.