Preparation of TI-1223 and TI-2223 superconducting films by spray pyrolysis

Abstract
Starting from nitrate solutions, precursors with composition Ba:Ca:Cu = 2:2:3 have been sprayed on MgO and LaAlO₃ single crystal substrates to form homogeneously distributed multiphase layers with a grain size smaller than 1 µm. Based on the knowledge of the Tl-Ba-Ca-Cu-O system, ex-situ thallination leading to TlBa₂Ca₂Cu₃O₂ (Tl-1223) and Tl₂Ba₂Ca₂Cu₃O₂ (Tl-2223) films, 1 to 2 µm in thickness, has been performed. SEM images reveal plate-like grains, 20 µm or more along the large dimension, and X-Ray diffraction experiments show that the films have both a c-axis and an in-plane texture more pronounced on LaAlO₃ than on MgO. The critical temperatures for Tl-1223 and Tl-2223 films are 113 K and 120 K, respectively, with transition width of about 2 K. The critical current densities J_c (77 K, 0 T), deduced from screening method, is above 7x10⁵ A/cm². The optimisation of the parameters conditioning the film fabrication and the properties are under work.