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

Ultrasonic spray pyrolysis technique has been used to deposit both in situ and ex situ high temperature superconducting films (HTSC) of Y₁Ba₂Cu₃O_x(YBCO) and Bi₂Sr₂CaCu₂O_x (BSCCO) compounds over various substrates. Nitrate precursor solutions are used to deposit films of ∼10 μm thickness. Both low temperature spray with substrate temperature T_s < 500 °C and high temperature deposition with T_s = 550-900 °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 ∼4 × 10⁴ A/cm² at 77 K and ∼ 10⁵ A/cm² 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.