Two series of samples with nominal compositions of Bi2+xSr2CuOy and Bi2Sr2−xCuOy (0 ⩽ x ⩽ 0.10) were prepared by a conventional solid-state reaction method. Laminar morphology is observed for all the samples under SEM. EDS analysis shows that Bi is slightly volatile, the depletion amount is about 3% in the Bi rich samples, but only about 1% loses in the Sr deficient samples. Hole concentration of the Bi2Sr2−xCuOy series increases with increasing x, showing a hole doping effect caused by the depletion of the Sr ions. In contrary, Bi2+xSr2CuOy series has a hole filling effect by introducing the extra Bi ions. These samples show metallic conducting behavior in the normal state and superconducting property at lower temperature. Tc decreases with increasing x on both series. Bi2Sr2CuOy has the highest Tc at 7.9 K with an optimal hole concentration of 0.237. Hole concentrations obtained from the O-K edge XANES spectra and the iodometric titration agree well in these samples.
Physica C: Superconductivity and its Applications 460-462 I, pp.422-423