New Pb-Based Cuprates with 1222 Structure Having No Tetravalent Ions, (Pb0.5Cu0.5)Sr2-xLn2-yLax+yCu2Oz (Ln: Gd, Dy, Ho and Er)

New Pb-based cuprates with 1222 structure have been synthesized in (Pb_0.5Cu_0.5)Sr_2-xLn_2-yLa_x+yCu₂O_z (Ln:Gd, Dy, Ho and Er) systems having no tetravalent ions such as Ce⁴⁺ and Pr⁴⁺. The composition to obtain an almost-single phase sample for each system was found to be located within a narrow limited region. After oxygen annealing at 500°C for 100 h under partial pressure of 100 atm, all the almost-single-phase samples were semiconductors, but a sample with the nominal composition of (Pb_0.5Cu_0.5)Sr_1.45Gd_1.95La_0.60Cu₂O_z among them showed a diamagnetic signal starting from about 20 K.