Structure and Superconductivity of Bi2(Sr2−xMx)CuO6 (M = La, Gd, Y) Compounds

C. Y. Lien ； H.-C. I. Kao ； D. C. Ling ； H. H. Lu ； J. M. Chen ； J. M. Lee

《Chinese Journal of Physics》 43卷3S期 (2005/06) Pp. 629-637

並列摘要

Single phase Bi2(Sr2−xMx)CuO6 (M = La, Gd and Y, abbreviated as 2201) compounds with 0 ≤ x ≤ 0.40 were prepared by a solid state reaction method. They all have orthorhombic symmetry and show laminar structure under SEM. EDS analysis shows that Bi is volatile and consequently the amount of Bi existing in the prepared sample is less than the starting nominal composition. All of the La-doped Bi-2201 compounds are superconducting with the highest Tc of 32 K for the x = 0.050 sample, which is optimal doped. The analysis of hole concentration deduced from the O K-edge X-ray absorption near edge structure (XANES) spectrum shows that the undoped 2201 is over doped and the samples for x ≥ 0.10 are underdoped due to the substitution of the M^3+ to the Sr^2+ cation. For the Gd-doped samples, the highest Tc (8 K) is also found in the x = 0.050 sample. Tc is strongly dependent on the radius of the dopant in the Sr site.