Effect of Fe Doping on the Structure and Superconducting Properties of (Ga,Co)Sr2(Tm,Ca)Cu2Oz

초록

To investigate the influence of Fe doping on the structure and the superconducting properties of (Ca,Co)-1212 cuprates, polycrystalline samples with nominal compositions of (Ga0.55Co0.45)Sr-2(Tm0.6Ca0.4)Cu2Oz (Ga0.55Co0.35Fe0.1)Sr-2(Tm0.6Ca0.4)Cu2Oz and (Ga-0.65 Fe-0.35)Sr-2(Tm0.7Ca0.3)Cu2Oz were prepared and examined by using neutron powder diffraction techniques and transport measurements. The Rietveld refinement data showed that all the samples crystallized in an orthorhombic structure with the symmetry of space group Ima2. In contrast to the Fe-free sample which showed superconductivity around 40 K, the superconductivity of the Fe-doped samples was rapidly suppressed as the Fe-doping content was increased. The (Ga0.65Fe0.35)Sr-2(Tm0.7Ca0.3)Cu2Oz sample exhibited a semiconducting behavior. The suppression in T-c observed for the Fe-doped samples is discussed in conjunction with the doping-induced structural changes in the charge reservoir blocks and the changes in the hole concentrations, in the Cu2Oz planes, which were estimated from both the bond-valence-sum calculations and the room-temperature thermoelectric powers.

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