Effect of Co Substitution on the Structure and Superconducting Properties of GaSr2(Tm,Ca)Cu2Oz

초록

The crystal structures of two samples with nominal compositions of GaSr(2)(Tm(0.7)Ca(0.3))Cu(2)O (z) and (Ga(0.65)Co(0.35))Sr(2)(Tm(0.7)Ca(0.3))Cu(2)O (z) have been analyzed by using neutron powder diffraction techniques to clarify the structural mechanisms associated with changes in superconducting behavior. Unlike for the Co-free sample, which does not show superconductivity, the Co-doped sample exhibits superconductivity around 45 K. The Rietveld refinement data reveal that both samples exhibit the 1212 structure with space group Ima2 and the Co atoms exclusively substitute for the Ga atoms in the GaO(4) tetrahedron located on the chain sites of the 123 parent structure. The improvement in T (c) of the Co-doped sample, compared to that of the undoped sample, is discussed in connection with the change in structural disorder and the change in hole concentration on the superconducting planes.

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