Crystal Structure of Sr-Ca-Cu-O: A Comparison Between That of Sr-Ca-Cu-O and of Bi-Sr-Ca-Cu-O
A new oxide-superconductor without rare-earth elements, Bi-Sr-Ca-Cu-O, has layered structure with alternative stacking of perovski te-1ike layers, consisting of Sr, Ca, Cu and O, and Bi2O2 layers. We are interested in the contribution of the Bi2O2 layer in this compound to the crystal structure that is closely related to superconductivity. In order to understand the role of the Bi2O2 layer in this type of superconductors, we synthesized Sr-Ca-Cu-O compounds and made a comparison between the structures of Sr-Ca-Cu-O and Bi-Sr-Ca-Cu-O.
The crystal structure of the samples was refined by the Rietveld analysis of their X-ray powder diffraction patterns. The crystal structure of Sr-Ca-Cu-O is much different from that of Bi-Sr-Ca-Cu-0. We have found zigzag band like structure consisting of Cu-O in Sr-Ca-Cu-O instead of Cu-O4 sheets in Bi-Sr-Ca-Cu-O. Bi-Sr-Ca-Cu-O synthesized from Bi2O3 and Sr-Ca-Cu-O powder by the solid state reaction showed superconductivity. This result suggests that the Bi2O2 layer plays an important role in forming the Cu-O4 sheets that is essential for the superconductivity of the high-Tc oxide-superconductors.
KeywordsElectrical Resistivity Constant Magnetic Field Rietveld Analysis Superconducting Oxide Bi202 Layer
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