Composition and superconductivity in single layer Bi-2201 phases

Several materials with nominal 2201 composition were prepared from various systems Bi_2+xSr_2-xCuO_6+z, Bi₂Sr_2-xCuO_6+z, Bi_2-xPb_xSr₂O_6+z, Bi_2.1-xPb_xCuO_6+z,Bi₂Sr_2-yLa_yCuO_6+z, Bi_1.9Pb_0.1Sr_2-yLa_yCuO_6+z, Bi_2-xPb_xSr_1.6La_0.4CuO_6+z and Bi_2.1-xPb_xSr_1.5La_1.4CuO_6+z in different gas atmospheres. According to the structural investigations the 2201 phase shows solid solution behaviour. However, irrespectively of the method of preparation the appearance of superconductivity is confined to multiphase material. Furthermore, the superconducting volume fraction is uniformly as low as ? 3%. The observed presence of trace superconductivity is easily explainable by small admixtures of superconducting foreign phases and in disagreement with the assumption of intrinsic superconducting properties of the Bi based 2201 phase.