A new high-temperature superconductor: Bi2Sr3-x Cax Cu2O8+y

Subramanian, M. A. ; Torardi, C. C. ; Calabrese, J. C. ; Gopalakrishnan, J. ; Morrissey, K. J. ; Askew, T. R. ; Flippen, R. B. ; Chowdhry, U. ; Sleight, A. W. (1988) A new high-temperature superconductor: Bi2Sr3-x Cax Cu2O8+y Science, 239 (4843). pp. 1015-1017. ISSN 0036-8075

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Official URL: http://www.sciencemag.org/cgi/content/abstract/239...

Related URL: http://dx.doi.org/10.1126/science.239.4843.1015


A new superconductor that displays onset behavior near 120 K has been identified as Bi2Sr3-xCaxCu2O8+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 Å, b= 5.414 Å, and c = 30.904 Å. The structure contains copper-oxygen sheets as in La2CuO4 and YBa2Cu3O7, but the copper-oxygen chains present in YBa2Cu3O7 do not occur in Bi2Sr3-xCaxCu2O8+y. The structure is made up of alternating double copper-oxygen sheets and double bismuth-oxygen sheets. There are Ca2+ and Sr2+ cations between the adjacent Cu-O sheets; Sr2+ 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 Bi2Sr3-xCaxCu2O8+y show a resistivity drop at about 116 K and apparent zero resistivity at 91 K.

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