Hg-based cuprate superconducting thin films prepared on CeO2 buffered R-plane sapphire substrate

Hg-Ba-Ca-Cu-O films have been grown on CeO2/R-plane sapphire substrates using a two-step process. First, a 200 nm thick Ba-Ca-Cu-(O, F) precursor film was prepared by sequential evaporation, then Hg-Re-Ba-Ca-Cu-O pellets as a source of Hg-vapour were applied using heat treatment. The prepared films were continuous with sufficient adhesion to the substrate and a maximum zero-resistance critical temperature of TC0=118 K. The x-ray diffraction measurements of all the prepared films confirmed the Hg-1212 phase as well as the minor Hg-1223 phase in some cases. We found that the best results were obtained at the mercuration temperature of 775 deg. C and an optimal annealing time within the range 0.5-5 h. The superconducting properties of the films prepared under unsuitable conditions were mostly improved after annealing in oxygen atmosphere. Darker parts of the film exhibited a different surface morphology and the presence of the Hg-1223 phase in plate-like grains. (author)