Effects of conversion parameters on the transport properties of YBCO films in the BaF₂ ex situ process

The effects of conversion parameters on transport properties of YBa₂Cu₃O_7-δ (YBCO) films on rolling assisted biaxially textured substrates (RABiTS) in the BaF₂ ex situ process were investigated for total pressures P_total between 0.1 and 1.3 atm, water vapor pressures P_H2O between approximately 7 and 70 Torr and processing temperatures T_S between 700 and 790°C. For this study, a 0.3-μm-thick Y-BaF₂-Cu-O precursor film was deposited on a 1-cm-wide Ni = 3 at.% W RABiTS with a buffer layer architecture of CeO₂YSZ/Y₂O₃/Ni deposited in single passes in various reel-to-reel systems for each layer. Under the conditions of P_total = 0.1 atm, T_S = 740°C and P_O2 approximately 150 mTorr, J_C > 2 MA/cm² was obtained at 77 K and self field for P_H2O ≤ 20 Torr. At higher P_H2O (= 70 Torr), however, the maximum attainable J_C decreased. In addition, the J_C at these higher P_H2O dropped rapidly with increased dwell time. The highest J_C, 2.5 MA/cm², was achieved at 730°C with P_total = 0.1 atm and P_H2O approximately 7 Torr. Finally, the variation of I_C with wet conversion time was performed at each processing temperature.