THE BISMUTH OXYCARBONATE BI2SR6-XCU3O10(CO3)2 - A NEW 40-K SUPERCONDUCTOR, 2ND MEMBER OF THE SERIES (BI2SR2CUO6)N(SR2CUO2CO3)N'

A new superconductor, Bi2Sr6-xCu(CO3)2O10, has been isolated for 0 less-than-or-equal-to x less-than-or-equal-to 1. This oxycarbonate exhibits a T(c,onset) of 40 K, with a Meissner volume fraction of 20%. The powder XRD and the ED study of this phase give evidence for an orthorhombic lattice with the following parameters: a=5.469 (2) angstrom, h=5.483 (2) angstrom and c=54.26 (1) angstrom; extra reflections, in incommensurate positions along b*, are observed corresponding to b' is similar to 9 x 5.5 angstrom. The HREM investigation shows that the structure of this phase corresponds to the intergrowth of double Sr2CuO2CO3 type layers with single Bi2Sr2CuO6 type layers. Thus, this oxide corresponds to the member ''n = 1, n'= 2'' of the structural series (Bi2Sr2CuO6)n(Sr2CuO2CO3)n'. It is compared to the 30 K superconductor Bi2Sr4Cu2O8CO3, first member of the series (n = n'=1).