Superconducting properties of ZnO-doped (Bi, Pb)-2223 thick film on Ni and NiO substrates prepared by spray deposition technique

The superconductivity of ZnO-doped (Bi, Pb)-2223 thick film on the Ni and NiO substrates, which was prepared by the spray deposition technique with cold forging, was investigated by characterizing the critical current density (J_c), the critical temperature (T_c), the orientation factor (f), and the microstructure of the film. The thickness of the thick film prepared by the spray deposition method was approximately 10 μm. The maximum J_c value of (Bi, Pb)-2223 film on NiO substrate was approximately 2200 A/cm² (I_c = 110 mA) when the film was sintered at 865 °C for 1 h with a cooling rate of 0.5 °C/min from 865 °C to 650 °C; in the case of Ni substrate, a maximum J_c value of approximately 2000 A/cm² (I_c = 100 mA) was obtained for the (Bi, Pb)-2223 thick film when a cooling rate was 3 °C/min. Such a difference in the J_c values of (Bi, Pb)-2223 thick film on Ni and NiO substrates is attributed to the presence of reaction layer at the (Bi, Pb)-2223 and substrate interface. In addition, the variations in the orientation factor of (Bi, Pb)-2223 thick film on NiO substrate related to those of J_c values. The J_c values of (Bi, Pb)-2223 film on NiO substrate with ZnO doping extremely depended on the amount of ZnO doping and the 0.5 wt% ZnO-doped (Bi, Pb)-2223 thick film deposited on NiO substrate, which was sintered at 835 °C for 1 h in air with a cooling rate of 1 °C/min, showed a J_c value of approximately 1200 A/cm² (I_c = 60 mA). Thus, it is considered that a small amount of ZnO doping was effective in lowering the sintering temperature of (Bi, Pb)-2223 thick film, resulting the improvement in the intragranular weak bonding or Josephson junction.