The Effect of the CeO₂ Buffer Layer Thickness on the J_c of YBa₂Cu₃O₇ Films Prepared on CeO₂/YSZ/CeO₂ Buffered Ni-electroplated Cu Tapes

Abstract

We investigated the effect of the CeO₂ buffer layer thickness on YBCO films prepared on CeO₂/YSZ/CeO₂-buffered Ni-electroplated Cu tapes. The thickness of the CeO₂ layer was found to be critical. The thickness of the CeO₂ seed layer was varied to be from 80 to 300 nm and the thickness of the CeO₂ cap layer was varied to be from 40 to 80 nm. To avoid the formation of cracks, we found that the thicknesses of the CeO₂ seed layer and CeO₂ cap layer must be less than 80 nm and 40 nm, respectively. Detailed SEM and AFM observations indicated a possible relation between the cause of crack formations and the thermal expansion coefficient differences of the films and the substrate. A smooth, continuous and crack-free surface was obtained on CeO₂ (40 nm)/YSZ/CeO₂ (80 nm) Ni-electroplated Cu tape. The YBCO films prepared on the CeO₂/YSZ/CeO₂-buffered Ni-electroplated Cu tapes revealed a transport J_c exceeding 3.6 MA/cm² at 77 K in a self-field.