A bismuth manganite with the ''2212'' structure: Bi2-xPbxSr1.5Ca1.5Mn2O9-delta

A manganite Bi2-xPbxSr1.5Ca1.5Mn2O9-delta, with the 2212 structure, has been synthesized for the first time. Its structural study by powder X-ray diffraction and by electron microscopy has been performed for two compositions, x = 0.5 and x = 1. The average structure consists of double perovskite layers (P) involving MnO6 octahedra and MnO5 pyramids intergrown with distorted triple rock salt layers (RS). The perovskite cages are mainly occupied by strontium so that these phases can be formulated [Bi2-xPbx Ca1.33Sr0.67](RS)[Sr0.83Ca0.17](P)Mn2O9-delta. The HREM investigation shows that the composition x = 0.5 exhibits an incommensurate modulated structure similar to that observed for the superconducting bismuth cuprate and for the iron-based 2212 compound, In contrast, the composition x = 1 does not exhibit any modulation, Although they are rare, some extended defects are observed especially for BiPbSr1.5Ca1.5Mn2O9-delta. Both oxides are semiconductors. (C) 1997 Academic Press.