Current limiting properties of superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ films on various substrates

The current limiting properties of textured and epitaxial YBa₂Cu₃0₇ 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 evailution of current and electrical field during dc 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, ΔT_c(ind)=O.5K, J_c(77K,res.)=2-3.7MA/cm² and FWHM(005) = 0.2°. During voltage pulse measurements the highest values for the dissipated power P_max/A=2.6MW/m², voltage U_max/l= 10.9 V/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 ∼4μsec and within lmsec the current was reduced to values below I_c2Cu₃O₇ on polycrystalline Al₂O₃ and YSZ are T_c,off(ind)=87K, ΔT_c=2K, J_c(77K)= 0.2MA/cm^{2 and FWHM(005)=0.9° yielding P_max/A=O.7MW/m₂, U_max/l=6.5 V/cm, R_max/R_o=1.4 (T_max≈500K) and reaction times of ∼10msec.}