High-I_c processing for YBCO coated conductors by TFA-MOD process

YBCO films were fabricated on PLD-CeO₂/IBAD-Gd ₂Zr₂ O₇/Hastelloy substrates using the TFA-MOD process. In order to obtain higher I_c performance, the thicker films maintaining high-J_c values are required. J_c depended strongly on the PH2O during the crystallization in the process. The pore size was smaller in the high-J_c films crystallized under the medium PH2O condition and became larger in the low-J_c films under both lower and higher PH2O for the YBCO films with a constant thickness. Furthermore, crack generation was observed in thick films crystallized at the high PH2O condition. Consequently, both pore and crack formations limit the J_c properties since large pore causes local reduction of current paths and additionally results in local concentration of electric fields. J_c also depended strongly on the YBCO crystal grain alignment which is affected by in-plane grain alignment of the buffered substrate. Then, the effect of in-plane grain alignment of the CeO₂ cap layer on J_c was investigated for thicker YBCO films. As a result, the J_c value increased with improvement of the crystal alignment of the CeO₂ cap layers. Finally, a YBCO film with a high-I_c value of 413 A at 77 K in self-field was achieved in a film fabricated on Δφ = 4° of the CeO₂ layer using the appropriate crystallization conditions for crack-free film.