Abstract
Superconducting Y-Ba-Cu-O films have been prepared by on-axis DC magnetron sputtering from single sintered targets with various compositions, and relationships of transition temperature Tc to film composition and c-axis lattice parameter c0 have been examined. Films with zero-resistance transition temperature Tc, end exceeding 85K are easily obtained using Ba-poorer targets than stoichiometry under the conditions of lower oxygen pressures, 3-10mTorr, than those reported by other investigators. The Tc and c0 of these films strongly depend on X-ray intensity ratio Cu/Ba which has been obtained directly by EDX and is related to film composition ratio. As the Cu/Ba ratio is decreased from an optimum value, Tc values rapidly decrease and c0 values increases. Moreover, the c0 values are influenced by X-ray intensity ratio Ba/Y. Although some films with higher Ba/Y ratios have c0 values larger than 11.82Å (=tetragonal lattice parameter of bulk), they still show superconductivity. Their dependence of Tc on c0 is clearly different from that usually reported for bulk samples and post-annealed films. On the basis of these results, effects of oxygen pressure during sputter-deposition on Tc, film composition and c0 are discussed.
