EFFECT OF SELECTIVE SUBSTITUTION ON THE MICROSTRUCTURE AND PROPERTIESOF BI2SR2CA2CU3O10 SUPERCONDUCTOR

Selective doping on Bi, Sr and Cu sites in Bi-Sr-Ca-Cu-0 superconducto rs were made and the resulting materials were characterized by 1. C. P ., resistivity measurements, X-ray diffraction, Infrared and Raman mic ro-spectroscopy, etc .... In barium doped materials Bi2Sr2-xBaxCa2Cu3O y with initial x0 varying from 0 to 0.5, only very few bismuth sites a re found to be affected by substitution; the pyramids remain in stagge red positions along the c axis. The substitution of Ba in Sr sites lea ds to a lowering of the Bi-O stretching frequencies along the c axis, both in Raman and Infrared spectra as the Ba dopant amount increases. This is in agreement with a redistribution and lengthening of the Bi-O distances along the c axis. X-ray diffraction supports this conclusio n in showing an expansion of the lattice parameter c from 37.12 Ain Ba rium free material to 37.19 Ain heavily Barium doped (x = 0.25) materi als. The re-appearance of the Raman doublet at 650-630 cm-1 with Ba do ping indicates an increase in structural modulation compared to Ba fre e (Bi/Pb)2223. These results are analyzed in comparison with those obt ained on selective substitution on bismuth sites with Pb, and on coppe r sites with lithium.