Optimization of the BaZrO3 concentration in YBCO films prepared by pulsed laser deposition

YBCO films were prepared by pulsed laser deposition from nanocrystalline targets doped with different concentrations of BaZrO3 ranging from c = 0.9 to 9.0 wt%. The critical temperature of the films decreases almost linearly with increasing BaZrO3 content whereas the critical current density shows a maximum near 3.9 wt%. In comparison with undoped YBCO films the accommodation field B* is considerably enhanced and the critical current density is improved in high fields in the films doped with BaZrO3, e.g. for c = 3.9 wt% by factor of 4.5 in a field of 5 T at 5 K. In the doped films the BaZrO3 particles grow epiaxially with YBCO. Transmission electron microscopy results show that the density of the BaZrO3 particles increases with increasing doping but the particle size remains practically the same (5-10 nm).