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 us ing a two-step process. First, a 200 nm thick Ba-Ca-Cu-(O, F) precursor fil m 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 ze ro-resistance critical temperature of T-Co = 118 K. The x-ray diffraction m easurements of all the prepared films confirmed the Hg-1212 phase as well a s the minor Hg-1223 phase in some cases. We found that the best results wer e obtained at the mercuration temperature of 775 degreesC and an optimal an nealing time within the range 0.5-5 h. The superconducting properties of th e films prepared under unsuitable conditions were mostly improved after ann ealing in oxygen atmosphere. Darker parts of the film exhibited a different surface morphology and the presence of the Hg-1223 phase in plate-like gra ins.