Analytical electron microscopy of high-T_c superconductors in the (Bi, Pb)-Ca-Sr-Cu-O system

Superconductors in the Bi-Ca-Sr-Cu-O system containing a small amount of Pb were investigated by analytical electron microscopy as well as high-resolution electron microscopy. X-ray spectroscopy analysis showed that most of grains in the samples contain approximately the same amount of Pb, and the compositions of the grains with the low-T_c (60 K) phase correspond to (Bi, Pb)_1.1(Ca, Sr)_1.4Cu_1.0O_x. The compositions of the samples containing high-T_c phase differ from grain to grain but indicate higher Cu atomic fraction than that of the low-T_c phase. High resolution electron microscope images directly reveal the modulated structure along the [010] direction with an incommensurate period which is the same as that observed in Bi-Ca-Sr-Cu-O. Electron energy loss spectra were also investigated by means of parallel detection system. The position and shape of the strong peak above the threshold at the oxygen K-edge were discussed relative to data for YBa₂Cu₃O_x.