Superconducting Properties of Magnetron Sputtered High T(sub C) Thin Films Containing Oxide Compounds of Yttrium, Bismuth, or Thallium

摘要

We have used multiple source magnetron sputtering to prepare thin films of Y-Ba-Cu-O, Bi-Ca-Sr-Cu-O, and Tl-Ca-Ba-Cu-O on (100) SrTiO sub 3 , (100) MgO, and ZrO-9%Y sub 2 O sub 3 substrates. Y-Ba-Cu-O films grow best on SrTiO sub 3 with mostly an a-axis orientation. Stoichiometry, particularly the Ba/Cu ratio must be within 2% of the correct value to obtain narrow delta T/sub c/ transitions. Conversely, the 80K phase of Bi-Ca-Sr-Cu-O films grows best on MgO substrates and has a predominant c-axis orientation. The requirements on composition are less stringent, however, the annealing temperature must be held within a narrow range around 865/degree/C to obtain the best films. The best films of Tl-Ca-Ba-Cu-O compounds are grown on (100) oriented and polycrystalline ZrO sub 2 substrates. The highest transition temperature, T/sub c0/, where the resistance goes zero is about 114K in the Tl sub 2 Ba sub 2 Ca sub 2 Cu sub 3 O/sub x/ phase and 100--105K in Tl sub 2 Ba sub 2 Ca sub 1 Cu sub 2 O/sub x/ and Tl sub 1 Ba sub 2 Ca sub 2 Cu sub 3 O/sub x/ phase samples. The upper critical field measurements show high anisotropies in the critical field slopes (greater than or equal to 70 for Tl-Ba-Ca-Cu-O compounds and approx.15 for Bi-Sr-Ca-Cu-O compounds), as might be expected from highly oriented materials. We will compare the preparation conditions and superconducting properties, including T/sub c/, delta T/sub c/, dB/sub c2//dT (parallel and perpendicular to film surface), of all three compounds. 17 refs., 6 figs. (ERA citation 14:007034)