Synthesis and crystal chemistry of a new manganite member Bi3.6Sr12.4Mn8O28+delta, n = 2 of the [Bi2Sr2MnO6](n)[Sr8Mn6O16+delta]-related 'tubular' family

摘要

A manganite with a "tubular" structure derived from the 2201-type, Bi3.6Sr12.4Mn8O28+delta, has been synthesized. Hts complex crystal chemistry has been studied using XRD, ND, and HREM techniques. It crystallizes in an orthorhombic cell, space group Pbnb, with a = 5.4946 Angstrom, b = 23.595 (1) Angstrom, and c = 23.580(1) Angstrom. This structure can be described as an intergrowth, along b, of two types of (010) slices: "2201"-type slices [Bi2Sr2MnO6] that are two octahedra thick and manganese-dieficient perovskite-related slices [Sr8Mn6O16+delta] that are one octahedron thick. A similar stacking is observed along c, which endows the structure with a pseudotetragonal character. Another may to describe this structure is to consider criss-crossing layers of manganese polyhedra forming tubes, where the [BiO] rows are inserted, and oxygen-deficient pillars, built up of four Mn polyhedra. This phase represents the n =2 member of a new "tubular" family [Bi2Sr2MnO6](n)[Sr8Mn6O16+delta]. Intergrowth and shearing mechanisms arise along the b and c directions, in agreement with the pseudotetragonal agonal character of the structure. The investigation of the transport and magnetic properties of this new manganite shows that it is an insulator and exhibits weak antiferromagnetism at ion; temperature (theta p = -650 K); the high-temperature data evidence an effective magnetic moment of 4.7 mu(B) characteristic of high-spin Mn3+ (mu(th) = 4.9 mu(B)). (C) 1998 Academic Press. [References: 22]