Superconductivity of the Pb-3212 compound in the Pb-Sr-La-Cu-O system and resistivity of the compound substituted by Ca

Superconducting phase with an onset near 60 K has been discovered in the Pb 2Sr3-xLaxCu3Oz system without Ag-doping. The optimum superconducting onset is obtained for a sample with the nominal composition of Pb2Sr2.5La0.5Cu3Oz . From X-ray diffraction and magnetic susceptibility measurements, it becom es clear that superconductivity results from the Pb-3212 phase, though the sample is not of the single phase. Then, almost the single 3212-phase sampl e and the samples substituted by Ca are obtained, but they are all semicond uctors. The temperature dependences of the resistivity for these samples su ggest that the transport process is follow ed by a three-dimensional variab le range hopping conduction. (C) 2001 Elsevier Science B.V. All rights rese rved.