DEPENDENCE OF J(C) ON THE COMPOSITION OF SUPERCONDUCTOR FILMS OF THE BI SYSTEM

In order to elucidate the effect of metal composition on the critical current density, J(c) of Bi system, the measurement of J(c) was carrie d out on highly oriented films of Bi2212 with a varied strontium conte nt 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 J(c) with t emperature, probably due to flux creep. J(c) was also found to be much more sensitive to the film composition than to T-c. The highest value of J(c), 1.4 x 10(5) A/cm(2), was observed for Bi2.1SrxCaCu2Oy with x = 1.85 at 4.2 K. The dependence of J(c) on the film composition is di scussed in reference to the peculiar species of excess oxygen and cati on vacancies.