Superconductivity in Bi-Sr-Ca-Cu-O (invited)

Abstract

We report on the structure and superconducting properties of a single phase polycrystalline composition given by Bi2.2Sr1.7Ca 1.2Cu2O8+δ as well as measurements on single crystals. X-ray and electron diffraction analyses of both single-crystal and single phase materials show an incommensurately modulated orthorhombic superlattice, derivable from a pseudotetragonal substructure. The various compositions have the common feature that the major portion of the superconductivity disappears above 85 K but there is a small tail in the diamagnetic susceptibility extending to 110 K, above which the sample becomes paramagnetic. Single crystals, grown by the flux method, exhibit the same incommensurately modulated pseudotetragonal structure as the ceramic, but show a higher diamagnetic shielding and in some cases also have tails. The critical currents in the (ab) plane are only about one-fifth of the value found for YBa2Cu3O7 crystals and the anisotropy is smaller. These reduced values may be an intrinsic property of the modulated superlattice but more likely are due to stacking faults and other defects in the crystals.