New Pb‐based layered cuprate superconductors

Two kinds of superconducting Pb‐based layered copper oxides, (Pb, Cu)Sr2(Y,Ca)Cu2O7 (the ‘‘1222’’ phase) and (Pb,Cu) (Ln,Ce)2 (Sr,Ln)2Cu2O9 (Ln: rare‐earth element; the ‘‘1212’’ phase), are synthesized and characterized. Although most of previously‐known Pb‐based cuprate superconductors form in a midly reducing atmosphere, these compounds form in an oxidizing atmosphere. Single‐phase ceramics of the ‘‘1212’’ compounds are obtained in the compositional range of (Pb1+x)/2Cu(1−x)/2)Sr2(Y1−xCax)Cu2Oz (x=0∼0.35 and z=∼7). The Pb‐based ‘‘1222’’ compounds are the first ‘‘1222’’ superconductor as well as the first superconducting lead cuprate containing ‘‘fluorite‐type’’ block layers. The maximum values of the observed superconducting onset temperatures are 65 K and 28 K for the ‘‘1222’’ phase and for the ‘‘1222’’ phase, respectively.