On the correlations between Sr:Ca substitution and structural modulation in the Bi-2212 phase

XPS and chemical titration both were carried out on Bi2+xSr1.8CaCu2Oz and Bi2Sr1.8−yCa1+yCu2Oz prepared by solid state reaction in order to investigate the correlation between the structural modulation and the mutual substitution of atoms. There was no clear evidence about the correlation between the modulation period by XRD and the site occupancies of Sr and Ca by XPS. However, there was a tendency that Bi mean valence by titration increased with increasing excess oxygen content and modulation period. The former one indicates the charge compensation and the latter one suggests the possibility of the origin of the structural modulation except for the excess oxygen.