SYNTHESIS AND TRANSPORT-PROPERTIES OF (BI, CU)-1212 CUPRATES EVIDENCEOF THE LOCALIZATION OF THE DOPED HOLES

Almost single-phase (Bi, Cu)-1212 samples, (Bi1-xCux)Sr2YCu2Oy with va rious oxygen contents were synthesized only in very narrow ranges of t he composition around x approximately 0.7, and with the sintering temp erature around 980-degrees-C. Although the resistivity decreased with increasing oxygen content, all the samples did not show metallic condu ctivity nor superconductivity. Compared with Bi-2212 cuprates, it was estimated that the density of doped hole carriers in the samples with high oxygen content was high enough to show superconductivity. It was confirmed that the doped carriers were localized by the observation of variable-range hopping conductivity and positive magnetoconducitivity . The origin of the localization in layered cuprates is discussed.