High critical current density YBa₂Cu₃O _7-δ thin films fabricated by ex situ processing at low pressures

There is interest in probing the feasibility and possible advantages of making uniform and cost-effective long-length coated conductors through a low-pressure processing approach. The low-pressure approach, eliminating the boundary layer and gas flow considerations, consumes much less of the processing gases and offers the possibility of improved uniformity and faster growth rate of superconducting films. Here, we have fabricated YBa₂Cu ₃O_7-δ (YBCO) epitaxial films of thickness 0.1-1.0 μm on SrTiO₃ single crystal substrates using ex situ post-deposition processing of co-evaporated Y, BaF₂ and Cu precursors in a controlled low-pressure gas mixture of oxygen and water vapour. Partial pressures of oxygen (P_O2) and water vapour (P_H2O) as low as 10 and 0.1 mTorr, respectively, were used. X-ray diffraction and scanning electron microscopy inspection were conducted for structure characterization of the films. High critical current densities (J_c) of ∼3.6 MA cm^-2 at 77 K in self-field were obtained, yielding properties comparable to those of in situ films and ex situ films processed under atmospheric pressure condition.