Measurements of critical currents as a function of temperature in YBa sub 2 Cu sub 3 O sub 7 sub - sub x thin films: a comparative study

J sub c for zero magnetic field is measured as a function of temp. in c-oriented thin layers of YBCO prepared by different synthesis methods. One direct and two indirect J sub c (T) methods are employed for each film. Results from the indirect measurements are calibrated against transport data. The investigation demonstrated the feasibility of using ac screening analysis in rapid determinations of J sub c (T) close to T sub c .