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

Abstract

YBCO films were fabricated on PLD-CeO2/IBAD-Gd2Zr2 O7/Hastelloy substrates using the TFA-MOD process. In order to obtain higher Ic performance, the thicker films maintaining high-Jc values are required. Jc depended strongly on the PH2O during the crystallization in the process. The pore size was smaller in the high-Jc films crystallized under the medium PH2O condition and became larger in the low-Jc 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 Jc properties since large pore causes local reduction of current paths and additionally results in local concentration of electric fields. Jc 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 Jc was investigated for thicker YBCO films. As a result, the Jc value increased with improvement of the crystal alignment of the CeO2 cap layers. Finally, a YBCO film with a high-Ic value of 413A at 77K 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.