Lead-doped Bi2Sr2CuO6: a superconductor free of modulation and superstructure

Abstract Crystals of lead-containing 2201 superconductor, (Bi 2− x Pb x )Sr 2 CuO 6 , were synthesized and characterized by electron microscopy XANES, X-ray diffraction, and electronic band structure calculations. Lead is present as Pb 2+ and the maximum value of x is approximately 0.25 ( T c ≈ 20 K). The crystal structure does not exhibit the modulations and superstructures seen in the lead-free Bi 2 Sr 2 CuO 6 superconductor. Bi/Pb-O “rock-salt” double layers consist of Bi/Pb-O chains containing 3-coordinated Bi/Pb atoms. Formation of these chains causes the CuO 6 octahedra of the CuO 2 sheets to buckle. It appears that substitution of Pb 2+ for Bi 3+ hinders the insertion of additional oxygen atoms into the double Bi-O layers such that lead-doped Bi 2 Sr 2 CuO 6 does not exhibit structural modulation.