Structural Analysis on Tc Variation of Bi2Sr2-xCa1+xCu2O8+y

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Abstract
The effects of heat treatment for Bi2Sr2-x Ca1+x Cu2O8+y (x=0.25, 0.5, 0.75, 1.0) were studied by X-ray diffraction and Raman scattering measurements. The curve of T c vs normal state conductivity ρ-1 is found to attain a maximum through heat treatment and a compositional change, suggesting the presence of an optimum hole concentration, as is observed in the La- and Y-based superconductors. In most cases, T c decreases with an increase in ρ-1, except for the sample with x=1.0. Furthermore, we found no peak shift of the 466 cm-1 Raman mode induced by the heat treatment and the compositional change, which are expected to vary the Bi-Cu distance.