The growth of YBCO films with high critical current at reduced pressures using the BaF2 ex situ process

The growth of 0.9-1.0 μm thick Y Ba2Cu3O7-δ (YBCO) films on biaxially textured Ni-3 at.% W (NiW) substrates using the BaF2 ex situ process was investigated at reduced pressures. By varying the water vapour pressure (PH2O), Y-BaF2-Cu-O (YBFCO) precursor films deposited by e-beam co-evaporation were converted at a reduced total pressure (Ptotal) of 50-55 Torr and conversion temperature (TS) of 740 deg. C for a wet conversion time (tW) of 60 min. Critical current density (JC) values greater than 1 MA cm-2 for the thick YBCO films were obtained under the condition of varying PH2O from low pressure to 10 Torr. The transition temperatures (TC) of the samples were over 90 K with ΔTC = 1.8-2.5 K. Pre-heat treatment of the precursor films on CeO2/Y SZ/Y2O3/Ni/NiW substrates under an O2 atmosphere condition before the conversion resulted in smooth surfaces without large secondary phase particles embedded in the films