Characterization of oxide superconductor by means of X-ray diffractometry and X-ray absorption near edge structure.

概要

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A new class of copper oxide superconductors, Y–Ba–Cu–O and Bi–Sr–Ca–Cu–O systems are investigated by using X-ray diffractometry (the Rietveld analysis) and X-ray absorption measurements (XANES) with a special attention to Cu–O configurations. It is shown that a significant difference of the Cu–O configuration is directly related to superconducting properties in both systems.(1) In the Y–Ba–Cu–O system, the structure of superconducting orthorhombic phase is characterized by a linear alignment of Cu–O as well as its planar network. The degree of linear ordering of oxygen atoms causes a continuous change both in a structure from tetragonal to orthorhombic phase and in the electronic state of copper atom.(2) In the Bi–Sr–Ca–Cu–O system, some superconductor phases are present. Each phase has its peculiar critical temperature Tc. The crystal structures contain a planar network of Cu–O and the sequence of the Cu–O layers is directly related to Tc. The electronic state of copper atoms in superconductor phase is nearly identical to that of orthorhombic Y–Ba–Cu–O system.
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