High JC YBCO films on biaxially textured Ni with oxide buffer layers deposited using evaporation and sputtering techniques

Epitaxial buffer layers of CeO₂ and Yttria-stabilized ZrO₂ (YSZ) have been deposited on biaxially textured nickel substrates using thermal reactive evaporation, electron beam evaporation and rf sputtering. The buffer layers were characterized by XRD, SEM and optical microscopy. YBCO films were deposited by high-pressure dc sputtering on CeO₂/YSZ/CeO₂ buffered substrates and the resulting superconducting properties were measured inductively. On exclusively evaporated buffer architectures critical current densities of 0.6 MA/cm² (77 K, H = 0 T) were measured. The buffers showed some cracks after YBCO deposition, which we considered to be responsible for the relatively low J_c. Buffer architectures with evaporated CeO₂ followed by rf sputtering of YSZ and CeO₂ in oxygen atmosphere remained completely crack free after YBCO deposition. Critical current densities between 1.5 and 2.3 MA/cm² (77 K, H = 0 T) in 460 nm thick YBCO films were obtained reproducibly. The critical temperatures T_c ranged between 88 and 92 K and the typical width ΔT_c of the transition was 1.5 K.