Influence of deposition rate on the properties of thick YBa₂Cu₃O_7-δ films

To investigate potential limits to the rate at which high-quality YBa₂Cu₃O_7-δ can be deposited, we have produced a series of 1 μm thick films by pulsed laser deposition on single-crystal SrTiO₃ substrates at average rates ranging from 2 Å/s to 240 Å/s. The critical current density of low-rate films was over 2 MA/cm² at 75 K, self field, but dropped linearly with rate to about 1 MA/cm² at the upper end of the range. In addition, the superconducting transition temperature, resistivity above the transition, and performance in an applied magnetic field were all degraded by increasing the deposition rate. A change in c-axis lattice parameter suggests that possible causes for this degradation are oxygen deficiency or cation disorder with the latter being the more likely. Annealing high-rate films at 790 °C for as little as 20 min improved critical current density to within 20% of low-rate values, and resulted in dramatic improvements in other film properties as well.