High-Jc thick YBCO coated conductors by TFA-MOD process

The TFA-MOD process was applied to fabricate YBCO films on PLD-CeO₂/IBAD-Gd₂Zr₂O₇/Hastelloy substrates. In order to obtain higher Ic performance, thicker films maintaining high J_c values are required. J_c depends strongly on the YBCO crystal alignment. Dependences of J_c on Δφ of the CeO₂ substrates has been investigated. It was found that the J_c value increased with improvement of the crystal alignment of the CeO₂ buffer layers. Also, the J_c value depended strongly on the P_H2O during the crystallization. The pore size in the film was smaller in the high J_c films fabricated under medium P_H2O and becomes larger in the low-J_c films under low and high P_H2O. Furthermore, crack formation was observed in thick films crystallized at high P_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_c properties. Finally, a YBCO film with 2.05 μm in thickness was fabricated on a CeO₂/Gd₂Zr₂O₇ layer buffered Hastelloy substrate with Δφ∼4°. A J_c value of 2.02 MA/cm² and transport I_c value of 413 A at 77 K, self-field were obtained.