PHASE-TRANSITIONS IN BI2SR2(CU1-ZFEZ)O-6+DELTA

We have investigated, by X-ray diffraction, a series of single crystal s of Bi-based oxides with the nominal composition Bi2Sr2(Cu1-zFez)O-6delta (0 less than or equal to z less than or equal to 0.55). In this system we observed two structural phase transitions with the increase of the doping content. The first transition, from an incommensurate mo noclinic phase to an incommensurate orthorhombic phase, occurs at a do ping content of iron z(Fe) =0.027. The second one corresponds to a pha se transition from an incommensurate orthorhombic phase to a commensur ate orthorhombic phase at z(Fe) = 0.34. The comparison of these result s with those for more limited substitutions of Zn and Ni indicates the significant role of the insertion of the extra oxygen in the (Bi-O)in finity double layers.