Superconductivity dependent on the amount of Bi and Sr in the Bi2Sr2CuO6 compounds

Abstract Two series of samples with nominal compositions of Bi 2+ x Sr 2 CuO y and Bi 2 Sr 2− x CuO y (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 Bi 2 Sr 2− x CuO y series increases with increasing x , showing a hole doping effect caused by the depletion of the Sr ions. In contrary, Bi 2+ x Sr 2 CuO y 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. T c decreases with increasing x on both series. Bi 2 Sr 2 CuO y has the highest T c 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.