Structural changes with lead substitution in Bi2-xPbxSr2CoO6

Structures refined for two members of the group of Bi2-xPbxSr2CoO6-type com pounds are proposed. For x = 0.16, the structure is incommensurately modula ted (a = 5.453(2) Angstrom, b = 5.426(2) Angstrom, c = 23.43(1) Angstrom. ( q) over right arrow(star) = 0.245(2)(b) over right arrow(star) + (c) over r ight arrow(star), F2mm(0 beta 1)00s). For x = 0.8, the modulation becomes v ery weak and has been neglected in the structural refinement (a = 5.3117(7) Angstrom, b = 5.4232(6) Angstrom, c = 23.590(2) Angstrom, Pnan). A new int erpretation of me undoped modulated Bi2Sr2CoO6 phase is given. A new type o f configuration for the [BiO] layers is confirmed and original modulation f eatures are elucidated in comparison with the related super-conducting cupr ate phases.