DOUBLE CATIONIC ORDERING IN THE 1201-SUBSTITUTED TYPE CUPRATE HGBISR7CU2SBO15

A new substituted cuprate, HgBiSr7Cu2SbO15, has been isolated; its str ucture has been determined by powder X-ray diffraction and high resolu tion electron microscopy. It crystallizes in the orthorhombic system w ith a = 7.6799(5) Angstrom approximate to 2a(p), b = 11.5549(7) Angstr om approximate to 3a(p), c = 8.8795(4) Angstrom approximate to c(1201) . This structure belongs to the 1201 type family, i.e., consists of si ngle perovskite octahedral layers intergrown with double rock salt lay ers. But its originality deals with a double cationic 1:2 ordering in the SbCu2 perovskite layers and Sr(Hg, Bi)(2) rock salt layers, leadin g to the formulation ([(Hg, Bi)(2)][SrO3][Sr3O3])(RS) (Sr3Cu2SbO9)(p). This correlated ordering between two kinds of layers is explained in terms of the size of the different metallic elements. The microstructu ral study shows that other types of ordering are observed locally in t he matrix. (C) 1995 Academic Press, Inc.