Dependence of Jc on the Composition of Superconductor Films of the Bi System

In order to elucidate the effect of metal composition on the critical current density, Jc of Bi system, the measurement of Jc was carried out on highly oriented films of Bi2212 with a varied strontium content and of Bi2Sr2(Ca1-xYx)Cu2Oy (BSCYCO) with a varied yttrium content grown on an MgO single crystal substrate by the spin coating-pyrolysis method. All the samples showed a considerable decrease in Jc with temperature, probably due to flux creep. Jc was also found to be much more sensitive to the film composition than to Tc. The highest value of Jc, 1.4×105 A/cm2, was observed for Bi2.1SrxCaCu2Oy with x=1.85 at 4.2 K. The dependence of Jc on the film composition is discussed in reference to the peculiar species of excess oxygen and cation vacancies.