CRYSTAL STRUCTURE AND SUPERCONDUCTIVITY OF Bi 2 Sr 2 CaCu 2 O 8 COMPOUND

The crystal structure of the ideal composition compound Bi 2 Sr 2 CaCu 2 O 8 with zero resistance temperature T c (0) = 81.4K had been determined by X-ray powder diffraction method. The basic structure of this compound exhibits tetragonal symmetry with lattice constants a = 3.825 ?, c = 30.82 ?. The most probable space group is D 4h 17 -14/mmm, Each unit cell contains two formula units. The arrangements of atoms in the unit cell are as follows:2Ca cations occupy 2(a) equivalent point position; 4Sr, 4Bi and 4Cu cations occupy the same equivalent point position 4(e) with respective parameters z= 0.110, 0.302, 0.445; 16O anions respectively occupy 8(g) (z = 0.445) and two 4(e) equivalent point positions (z= 0.210 and z = 0.380), The crystal structure of Bi 2 Sr 2 CaCu 2 O 8 can be derived from Aurivillius type structure. The main feature of the structure is alternate arrangement of cations along (00z) and (1/2, 1/2, z) of tetragonal system. The other possible superconducting phases in the Bi-Sr-Ca-Cu-O system can be considered as the structure having different stacking layers along z axis.