title: A New High-Temperature Superconductor: Bi2Sr3-x Cax Cu2O8+y.
abstract: A new superconductor that displays onset behavior near 120 K has been identified as Bi(2)Sr(3-x)Ca(x)Cu(2)O(8+y), with x ranging from about 0.4 to 0.9. Single crystal x-ray diffraction data were used to determine a pseudo-tetragonal structure based on an A-centered orthorhombic subcell with a = 5.399 A, b= 5.414A, and c = 30.904 A. The structure contains copper-oxygen sheets as in La(2)CuO(4) and YBa(2)Cu(3)O(7), but the copper-oxygen chains present in YBa(2)Cu(3)O(7) do not occur in Bi(2)Sr(3-x)Ca(x)Cu(2)O(8+y). The structure is made up of alternating double copper-oxygen sheets and double bismuth-oxygen sheets. There are Ca(2+) and Sr(2+) cations between the adjacent Cu-O sheets; Sr(2+) cations are also found between the Cu-O and Bi-O sheets. Electron microscopy studies show an incommensurate superstructure along the a axis that can be approximated by an increase of a factor of 5 over the subcell dimension. This superstructure is also observed by x-ray diffraction on single crystals, but twinning can make it appear that the superstructure is along both a and b axes. Flux exclusion begins in our samples at about 116 K and is very strong by 95 K. Electrical measurements on a single crystal of Bi(2)Sr(3-x)Ca(x)Cu(2)O(8+y) show a resistivity drop at about 116 K and apparent zero resistivity at 91 K.
authors.forename: M A
authors.initials: MA
authors.lastname: Subramanian
authors.forename: C C
authors.initials: CC
authors.lastname: Torardi
authors.forename: J C
authors.initials: JC
authors.lastname: Calabrese
authors.forename: J
authors.initials: J
authors.lastname: Gopalakrishnan
authors.forename: K J
authors.initials: KJ
authors.lastname: Morrissey
authors.forename: T R
authors.initials: TR
authors.lastname: Askew
authors.forename: R B
authors.initials: RB
authors.lastname: Flippen
authors.forename: U
authors.initials: U
authors.lastname: Chowdhry
authors.forename: A W
authors.initials: AW
authors.lastname: Sleight