STRUCTURE EVOLUTION IN SUPERCONDUCTING (HG0.7TL0.3)(2)BA-2(CA-X,Y-1-X)CU2O8-2-DELTA

Nearly single-phase superconducting (Hg-0.7, Tl-0.3)(2)Ba-2(Ca-x,Y-l-x )Cu2O8-2 delta samples (x = 0.1, 0.2, 0.4 and 0.6) were prepared by a high pressure synthesis technique. The crystal structure of these samp les was determined by X-ray Rietveld refinement. This crystal belongs to a tetragonal system and has a space group of 14/mmm with a approxim ate to 3.86 and c approximate to 29.0 Angstrom. The unit cell paramete r a decreases and c increases with increasing x. The expansion of the c-axis is found to mainly result from the increase in the inter-planar distance between the Ba-Hg planes. The present refinement does not sh ow evidence for the substitution of Cu in the (Hg,Tl) site.