MICROSTRUCTURE OF BI2212 AND (BI/PB)2212 SINGLE-CRYSTALS AND EFFECT OF ELECTRON-DONORS AND ACCEPTORS

Pure and lead doped Bi2Sr2CaCu2O8 (Bi2212) single crystals were grown an their structures were studied by several methods, especially by resistivity measurements, electron microprobe and Raman micro-spectroscopy. The microstructure and the Raman spectrum of Bi2212 were analyzed in comparison to those of Bi2201 and Bi2223 single crystals. In these structures, the existence of close, staggered and antiparallel Bi-O bonds leads to a Raman doublet al 653 and 627 cm-1 which corresponds to coupled motions in these bonds. The intercalation of iodine in Bi2212 suppresses this staggered configuration and gives a more homogeneous vertically aligned distribution of (Bi)O(Cu) bonds. In these intercalations, the presence of unsymmetrical I3- ion is demonstrated. Similar bond-ordering was observed on intercalation with chloranil and tetrahydrofuran. By lead doping, the staggered bonds are no longer identical and the decoupling leads to a single phonon around 623 cm-1 and confirms that Pb occupies Bi position.