New Non-Superconducting Layered Bi-Oxide Phases of Formula Bi2M3Co2Oy Containing Co Instead of Cu

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We report the cationic substitution of Cu by Co within the 85K Bi based high Tc oxides to produce new phases of general formula Bi2M3Co2Oy with M = Ca, Sr and Ba. Single crystals of these phases, grown using Co3O4 (excess) flux, were investigated for their structural, magnetic and electrical properties. The subcell appears similar to that of Bi2Sr2CaCu2Oy phase but the superstructure is more complicated due to the presence of a more complex incommensurate structural modulation. The substitution of Cu by Co is accompanied by an uptake of additional oxygen. With M = Sr or Ca, the compounds are semiconductors, whereas when M = Ba the compound is metallic above 100K, and semiconducting below 100K. The magnetic susceptibility varies little with temperature, and shows no magnetic transitions. Photoemission measurements show that Co is in a + 3 oxidation state with a low spin configuration.



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