Improved current transport properties of post annealed Y1Ba2Cu3O7−x thin films using Ag doping

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Abstract
The influence of Ag doping on the transport properties of Y1Ba2Cu3O7−x thin films prepared by Y, BaF2, and Cu co-evaporation and optimized ex situ post annealing has been investigated. Both undoped and Ag doped films have values of Tc above 90 K, but Jc (77 K) is highly dependent on the nominal thickness (tnom) of the as-deposited film. For undoped films with tnom≤300 nm Jc (77 K) (≫106 A/cm2) decreases monotonically with increasing film thickness. Above 300 nm Jc (77 K) decreases rapidly to values below 5×105 A/cm2. Ag doped films with tnom≥200 nm have higher Jc (77 K) values than those of undoped films. Ag doped films have a maximum in Jc (77 K) around 250 nm. As for the undoped films, there is a large decrease in Jc (77 K) for Ag doped films with tnom≥300 nm. It was found that the higher values of Jc (77 K) for the Ag doped films were due to a better epitaxial growth of the YBCO compound. The low values of Jc (77 K) for both undoped and Ag doped single layer films with tnom≥300 nm were found to be due to the absence of 1–2–4 inclusions in these films. Based on these findings high Jc (77 K) films with tnom≳300 nm were grown by successive deposition and annealing of films with tnom<300 nm on top of each other. A 2×150 nm undoped film was found to have a Jc (77 K) value of 4, 1×106 A/cm2. This is almost a doubling of the Jc (77 K) value as compared to the value for the 300 nm single layer undoped film (2,2×106 A/cm2). Ag doped double layer films of 2×150 nm and 2×215 nm had comparable Jc (77 K) values (5,8×106 and 5,6×106 A/cm2, respectively). In comparison with the undoped 2×150 nm film Jc (77 K) is thus further increased (by about 50%) when doping with Ag.