| Summary: | Bulk superconductivity was observed in the systems (Pb0.75 Cu0.25)Sr2(Ca1-xYx)Cu2O7 -δ and (InyPb0.75-yCu0.25)Sr2 (Ca0.5Y0.5)Cu2 O7-δ. With decreasing x in (Pb0.75Cu0.25)Sr2 (Ca1-xYx)Cu2O7-δ, Tc increases up to 55 K at x = 0.1; however this specimen is multiphasic with superconducting Meissner volume fraction of ca. 1.5%. In contrast, the sample with x=0.5 is nearly single phase and has a lower Tc (45 K) and a high superconducting Meissner volume fraction ca. 20.2%. An increase of the indium doping in (InyPb0.75-y Cu0.25 Sr2(Ca0.5Y0.5)Cu2O7-δ, 0 ≤ y ≤ 0.2, results in; n increase in the superconducting transition temperature from 45 K for y=0, to 60 K for y=0.2.
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