Novel 1122 thallium cuprates showing high T c superconductivity: TlCa 1−x Y,Ba 2 Cu 2 O y ,T, 1−x Pb x CaSr 2 Cu 2 O y and T l Ca 0.5 Ln 0.5 Sr 2 Cu 2 O y

Substitution of Ca by Y in TlCaBa 2 Cu 2 O y does not favour superconductivity, but substitution of Tl by Pb or of Ca by Ln (Ln = Y or rare earth) in TlCaSr 2 Cu 2 O y results in high T c superconductivity (T c π 60-90 K). TlCa 1-x Ln x Sr 2 Cu 2 O y is a new series of high T c superconductors, but the x = 0.0 composition does not exhibit bulk superconductivity.