Sequentially evaporated thin Y-Ba-Cu-O superconductor films: Composition and processing effects

Thin films of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} have been grown by sequential evaporation of Cu, Y, and BaF{sub 2} on SrTiO{sub 3} and MgO substrates. The onset temperatures were as high as 93 K, while T{sub c} was 85 K. The Ba/Y ratio was varied from 1.9 to 4.0. The Cu/Y ratio was varied from 2.8 to 3.4. The films were then annealed at various times and temperatures. The times ranged from 15 min to 3 hours, while the annealing temperatures used ranged from 850 {degree}C to 900 {degree}C. There was found a good correlation between transition temperature (T{sub c}) and the annealing conditions; the films annealed at 900 {degree}C on SrTiO{sub 3} had the best T{sub c}'s. There was a weaker correlation between composition and T{sub c}. Barium poor films exhibited semiconducting normal state resistance behavior while barium rich films were metallic. The films were analyzed by resistance versus temperature measurements and scanning electron microscopy. The analysis is of the films and the correlations are reported.