HIGH CRITICAL CURRENT DENSITIES IN YBA2CU3O7-X FILMS ON POLYCRYSTALLINE ZIRCONIA

We report the growth on polycrystalline yttria-stabilized zirconia substrates of YBa2Cu3O7-x films with J c (77 K)=11 000 A/cm2 and Jc (4.2 K)=122 000 A/cm2 by pulsed laser ablation. These Jc values are among the highest reported for YBa2Cu3O7-x on any polycrystalline substrate and approach the intrinsic upper limit for films with large-angle grain boundaries, as indicated by recent bicrystal experiments. We find that the substrate temperature during film growth is most important in obtaining high Jc polycrystalline films. Although the magnetic field dependence of Jc indicates the presence of weak links, the behavior of Jc (4.2 K, H) suggests that a percolative path consisting of low-angle grain boundaries exists in the films, resulting in Jc (4.2 K, 60 kOe)=4100 A/cm2.