The crystal structure and low-magnetic-field properties of the Pb- and Ba-doped Bi-Sr-Ca-Cu-O system

The XRD analyses for the Bi-Pb-Sr-Ca-Ba-Cu-O system show that the addition of Ba ions is favourable to the formation of the higher-T_c phase (T_c>100 K), and TEM observations show that the partial substitution of Ba ions for Ca ions induces a change in the crystal microstructure of the higher-T_c phase (T_c>100 K); a new modulation mode with a wavelength of 43 AA appears in the electron diffraction pattern of the higher-T_c phase. The EDS results confirm that Ba ions really intercalate into the crystal of the 2:2:2:3 phase. The DC magnetization measurements show that the sample displays a much larger hysteresis than that of a general Pb-doped sample. In addition, a study on the influence of low DC magnetic fields on the real component chi ' and imaginary component chi " of the susceptibility for the Ba-doped sample shows that T_p is related to the applied field H^DC and their relation can be fitted by (1-T_p/T_c) varies as H^0.23 when H ^DC<140 G, and (1-T_p/T_c) varies as H ^0.65 when H^DC>140 G. These data can be excellently interpreted in terms of Bean's critical-state model.