Superconducting Lead Cuprates Synthesized in Oxidizing Atmosphere

Two kinds of superconducting lead cuprates, (Pb,Cu)Sr2(Y,Ca)Cu2O7, (the “1212” phase) and (Pb,Cu)(Sr,Eu)2(Eu,Ce)2Cu2O9 (the “1222” phase), are synthesized and characterized. Although most of previously-known Pb-based cuprate superconductors form in a mildly reducing atmosphere, these two lead cuprates form in an oxidizing atmosphere. It is shown that single-phase ceramics of the “1212” lead cuprates are obtained for the chemical compositions of (Pb(1+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” superconductors and also the first superconducting lead cuprates containing “fluorite-type” block layers. The maximum values of the observed superconducting onset temperatures are 65 K and 28 K for the “1212” phase and for the “1222” phase, respectively.