Current limiting properties of superconducting YBa2Cu3O7 films on various substrates

The current limiting properties of textured and epitaxial YBa2Cu3O7 films with different thickness on various substrates (i.e. r-cut sapphire, polycrystalline Al2O3 and Y-stabilized ZrO2) are examined. The correlation between structural, morphological, superconducting properties and the evolution of current and electrical field during de and ac current pulses are determined. The best results are obtained in epitaxial YBa2Cu3O7 films on large-area CeO2/sapphire with a thin Au-top layer. They are characterized by T-c(ind)=88-90K, Delta T-c(ind)=0.5K, J(c)(77K,res.)=2-3.7MA/cm(2) and FWHM(005)=0.2 degrees. During voltage pulse measurements the highest values for the dissipated power P-max/A=2.6MW/m(2), voltage U-max/I=10.9V/cm, and R-max/R-o=2.33 and the highest mean temperature of the film of T-max=650-700K could be obtained. The maximum current of (2-6)I-c was reached after similar to 4 mu sec and within 1msec the current was. reduced to values below I-c both being an indication for the fast reaction time and homogeneity of the films. The best values for YBa2Cu3O7 on polycrystalline Al2O3 and YSZ are T-c,T-off(ind)=87K, Delta T-c=2K, J(c)(77K)=0.2MA/cm(2) and FWHM(005)=0.9 degrees yielding P-max/A=0.7MW/m(2), U-max/I=6.5V/cm, R-max/R-o=1.4 (T(max)approximate to 500K) and reaction times of similar to 10msec.