Abstract
Polycrystalline samples of (Nb1-xCux)Sr2EuCu2Oz with x = 0 (pure) and 0.1 ≤ x ≤ 0.5 (Cu-doped samples), and (Nb0.9-xTi0.1Cux)Sr2EuCu2Oz with x = 0 (Ti-doped sample) and 0.1 ≤ x ≤ 0.4 (Ti/Cu co-doped samples) were synthesized and characterized by means of powder X-ray diffraction (XRD), transport, and magnetization measurements. In the Ti-free Cu-doped samples and the Ti-doped sample, no superconductivity was observed in the resistivity measurements. In contrast, for the Ti/Cu codoped sample with x = 0.4, a superconducting transition was newly observed in both resistivity and magnetization measurements with Tc (onset) of about 30 K. Rietveld refinements of XRD data for the Ti/Cu co-doped samples showed that a structural transformation occurred from tetragonal (P4/mmm) phase to orthorhombic (Ima2) phase and the weight fraction of the orthorhombic phase increased upon increasing the Cu-doping content. The superconducting behaviors induced by Ti/Cu co-doping are discussed in conjunction with the change in hole concentration and the structural transformation.
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