CATION CHEMISTRY AND PHASE-RELATIONS IN THE SUPERCONDUCTING BI-PB-CA-SR-CU-O SYSTEM

The cation chemistry and magnetic susceptibility of a suite of samples in the superconducting (Bi,Pb)2Can -1Sr2CunOx system have been studied at various stages during their evolution from the two-layer to the high Tc three-layer polytype. Relationships between phase assemblage and cation chemistry have been identified in both relatively pure and interlayered samples. The Ca/Sr ratio is an important indicator of the relative proportion of the 30 and 37 Å phases. The cation defect structure of these (Bi,Pb)2Can - 1Sr2CunOx superconductors includes significant vacancies on the Bi and possibly the Sr layers. High cation vacancy concentrations, particularly in the two-layer-dominant material formed at early stages in processing, may play a key role during the subsequent two-layer → three-layer phase transformation. © 1990.