New T1‐based superconductor T1PbSrRCuO without Ca with Tc above 100 K

Ca‐free T1PbSrRCuO samples (R=rare earths) with Tc up to above 100 K were prepared, and studied by resistance and ac susceptibility measurements and by powder x‐ray diffraction analyses. A 1212‐type phase (Tl1−xPbx)Sr2(Sr1−yRy)Cu2Oz is responsible for the observed supercondcutivity. A rare‐earth is required for the formation of the 1212 phase. Pb‐dopping is necessary to increase the Tc of the 1212 phase from 90 K to above 100 K.