The effect of excess Ca2PbO4 on the superconducting properties of Bi1.7Pb0.3Sr2Ca2Cu3 OyBx (B ≡ Ca2 PbO4) is investigated through X-ray diffraction, resistivity and a.c. magnetic susceptibility measurements. The Xpray diffraction results show that the volume friction of the low Tc (221s) phase decreases and that of (2223) phase increases with the addition of Ca2PbO4. For x = 0.6 and 1.5, only the (2223) phase exists. At higher Ca2PbO4 concentrations, i.e. for x = 3.0, the low Tc phase again appears along with the high Tc phase. Diffraction peaks appear at d = 2.02, 2.814 and 2.85, which are characteristic peaks of Ca2PbO4, and their intensities increase with increasing x, indicating that Ca2PbO4 exists in the lattice in the same form. However, the Tc(0) values decreased gradually from 107 to 98 K with increasing Ca2PbO4 concentration. Compared with the undoped sample, the width of the transition δTc is broad for impurity-added samples and reaches a maximum value for x = 3.0. Pure and Ca2PbO4-doped samples showed two peaks in ξ″ vs. T curves and two steps in ξ′ vs. T curves. The first peak is close to the transition temperature and corresponds to the midpoint of the first step in the ξ′ curve. The second peak appears below 98 K and this peak maximum corresponds to the midpoint of the second step. The position of both sets of peaks remained almost the same up to x = 1.5 and shifted towards lower temperatures thereafter. The role of Ca2PbO4 in the growth of the (2223) phase and the mechanism of energy loss are discussed.
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