We investigated the effect of the CeO
2 buffer layer thickness on YBCO films prepared on CeO
2/YSZ/CeO
2-buffered Ni-electroplated Cu tapes. The thickness of the CeO
2 layer was found to be critical. The thickness of the CeO
2 seed layer was varied to be from 80 to 300 nm and the thickness of the CeO
2 cap layer was varied to be from 40 to 80 nm. To avoid the formation of cracks, we found that the thicknesses of the CeO
2 seed layer and CeO
2 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 CeO
2 (40 nm)/YSZ/CeO
2 (80 nm) Ni-electroplated Cu tape. The YBCO films prepared on the CeO
2/YSZ/CeO
2-buffered Ni-electroplated Cu tapes revealed a transport
Jc exceeding 3.6 MA/cm
2 at 77 K in a self-field.
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