Oxygen order control by post-annealing for optimizing critical temperature of YBaCuO coated conductors with silver protective layer

Oxygenation is one of the most essential processes for practical applications of REBa2Cu3O7−δ (RE123, RE = Y, Gd etc. rare earths) superconductors. Second generation high-Tc superconducting coated conductors are based on biaxial textured RE123 thin films, on which, a cover layer of silver for protecting is normally applied. It results in a little more complicated oxygenation process compared to naked film without silver protective layer. In the present work, a series of absorbing oxygen post-annealing processes were carried out for YBa2Cu3O7−δ coated conductors. The oxygen diffusion procedure and the kinetics in the annealing process were investigated. Analysis and calculations show that the activation energy was 1.01 eV, consistent with previous reports. Moreover, experiments show that the “over-doping” phenomena frequently occurs in coated conductors, and thus dropping the Tc to as low as 86-88 K. To improve the temperature margin for practical applications (temperature difference between the superconducting transition temperature Tc and application temperature), we investigated the potential of increase in Tc by preventing from the “over-doped” happening, while keeping oxygen in order. Finally, by employing the new annealing process, we can produce long (several hundred meters) coated conductor with high Tc,onset (92 K), narrow transition width and stable performance.