Composition-induced superconductivity (up to 55 K) in the system (Pb_0.75Cu_0.25)Sr₂(Ca_1-xY_x)Cu₂O_7-δ

We demonstrate a compositionally induced superconductor-to-semiconductor transition in the system (Pb_0.75Cu_0.25)Sr₂(Ca_1-xY_x)Cu₂O_7-δ. Superconducting behavior is observed over the composition range 0.1 ≤ x ≤ 0.6. Samples with 0.1 ≤ x ≤ 0.3 are multiphasic, but the superconducting transition temperature is a maximum (55 K) over this range of compositions. The sample having x = 0.5 gives rise to an acceptable phase purity, a superconducting transition temperature of 45 K, and the maximum superconducting (Meissner) volume fraction (20.2%). A superconductor-to-semiconductor transition occurs at x = 0.7.