Low cost synthesis of high-T_c superconducting films on metallic substrates via ultrasonic spray pyrolysis

摘要

Ultrasonic spray pyrolysis technique has been used to deposit both in situ and ex situ high temperature superconducting films (HTSC) of Y_1Ba_2Cu_3O_x(YBCO) and Bi_2Si_2CaCu_2O_x (BSCCO) compounds over various substrates. Nitrate precursor solutions are used to deposit films of approx 10 mu m thickness. Both low temperature spray with substrate temperature T_s < 500 deg C and high temperature deposition with T_s = 550-900 deg C are carried out. Superconducting properties of these films are observed to vary with various parameters such as concentration of spray solution, deposition temperature and nature of substrate and annealing process. Best quality films show T_c (R = 0) of 89 K and J_c of approx 4 X 10~4 A/cm~2 at 77 K and approx 10~5 A/cm~2 at 20 K. X-ray diffraction pattern reveals that the films are textured along c-axis. Successful attempt has been made to deposit in situ superconducting films over polycrystalline Ag for coated conductor applications. Various deposition and annealing conditions are optimized to control the diffusion of Ag from substrate to film, which otherwise can segregate into the grain boundaries and make the films non-superconducting.