Epitaxial superconducting Tl_0.5Pb_0.5Sr_1.6Ba_0.4Ca₂Cu₃O₉ films on LaAlO₃ by thermal spray and post-spray annealing

A simple, low-cost and easily scalable method - thermal spray followed by post-spray annealing - has been successfully demonstrated for fabricating high-J_c epitaxial superconducting films of Tl_0.5Pb_0.5Sr_1.6Ba_0.4Ca₂Cu₃O₉ [(Tl, Pb)-1223]. The process was performed by spraying a stoichiometric solution containing Tl, Pb, Sr, Ba, Ca and Cu nitrates onto LaAlO₃ substrates heated to 300-400 °C. Subsequently, the amorphous films were placed inside a silver containment along with two semicircular unfired pellets, and were reacted and crystallized by a thermal anneal at 870 °C in air. X-ray diffraction showed that the films consist mainly of c-axis aligned (Tl, Pb)-1223 phase with a small amount of (Tl, Pb)-1212 phase. X-ray φ-scans revealed very good epitaxial growth. Four-probe transport measurements on a 4 mm wide and 1.2 μm thick film showed a superconducting transition temperature of 106-109 K, with a zero-field critical current of 51 A at 77 K, which corresponds to a critical current density of 1.1×10⁶ A cm^-2.