High-Jc Thick YBCO Coated Conductors by TFA-MOD Process

Abstract

The TFA-MOD process was applied to fabricate YBCO films on PLD-CeO/sub 2//IBAD-Gd/sub 2/Zr/sub 2/O/sub 7//Hastelloy substrates. In order to obtain higher Ic performance, thicker films maintaining high J/sub c/ values are required. J/sub c/ depends strongly on the YBCO crystal alignment. Dependences of J/sub c/ on /spl Delta//spl phi/ of the CeO/sub 2/ substrates has been investigated. It was found that the J/sub c/ value increased with improvement of the crystal alignment of the CeO/sub 2/ buffer layers. Also, the J/sub c/ value depended strongly on the P/sub H2O/ during the crystallization. The pore size in the film was smaller in the high J/sub c/ films fabricated under medium P/sub H2O/ and becomes larger in the low-J/sub c/ films under low and high P/sub H2O/. Furthermore, crack formation was observed in thick films crystallized at high P/sub H2O/. The large pore causes local reduction of current paths and additionally introduces the concentration of electric fields. It was found that both the porosity and crack formations limit the J/sub c/ properties. Finally, a YBCO film with 2.05 /spl mu/m in thickness was fabricated on a CeO/sub 2//Gd/sub 2/Zr/sub 2/O/sub 7/ layer buffered Hastelloy substrate with /spl Delta//spl phi//spl sim/4/spl deg/. A J/sub c/ value of 2.02 MA/cm/sup 2/ and transport I/sub c/ value of 413 A at 77 K, self-field were obtained.