SUPERCONDUCTIVITIES IN THE (BI,PB)-OXYCARBONATE SYSTEM

Two (Bi,Pb)-oxycarbonate superconductors have been found by resistivit y and magnetization measurements. Transition temperatures are 41 K (54 K) for the low-T(c) phase (high-T(c) phase). The crystal structures w ere analyzed by using the HRTEM and X-ray diffraction techniques. The lattice parameters were a0 = 3.821 angstrom, c0 = 39.444 angstrom (a0 = 3.88 angstrom, c0 = 54.52 angstrom) for low-T(c) phase (high-T(c) ph ase) in the tetragonal unit cell. A crystal structure model is propose d in which the chemical formula for the low-T(c) phase (high-T(c) phas e) is (Bi,Pb)2Sr4Cu2CO3O8 ((Bi,Pb)2Sr6Cu3(CO3)2O10), which can be desc ribed as the combination of a single (double) Sr2CO3 block and a singl e (Bi,Pb)2Sr2O4 block.