Abstract :
Single-phases of Pb-substituted Bi–Ca–Co–O misfit-layer cobaltites with various Pb concentrations have been synthesized and the Pb-substitution effects on the structural, electrical and magnetic properties have been systematically investigated. Powder X-ray diffraction analysis showed that the single-phases of Bi1.8−x/2PbxCa2Co2Oz were obtained up to x = 0.6 – 0.7 under the optimized synthesis conditions. The lattice parameters of Bi1.8−x/2PbxCa2Co2Oz continuously changed with increasing Pb concentration. The electron diffraction analysis suggested that the structure consisted of two different sublattices with a rock salt structure (RS) and a hexagonal CdI2 structure (H), respectively, without modulation. In combined with the chemical composition analysis, the chemical formulas of the x = 0 and x = 0.6 samples were determined approximately as [Bi1.74Co0.31Ca2.01O4]RS[CoO2]1.69 and [Bi1.47Pb0.38Co0.29Ca1.98O4]RS[CoO2]1.71, respectively. The electrical resistivity became more metallic with increasing the Pb concentration up to x = 0.6 . Moreover, the Pb-substitution simultaneously increased the antiferromagnetic Weiss temperatures and decreased the effective magnetic moments of the Co ions.
