A new cobaltite with a tubular structure: Bi{sub 3.7}Sr{sub 11.4}Co{sub 8}O{sub 28{minus}{delta}}, the n = 2 member of the series [Bi{sub 2}Sr{sub 2}CoO{sub 6}]{sub n}[Sr{sub 8}Co{sub 6}O{sub 16{minus}{delta}}]
- CNRS UMR, Caen (France). Lab. CRISMAT
A cobaltite, Bi{sub 3.7}Sr{sub 11.4}Co{sub 8}O{sub 28{minus}{delta}}, with a tubular structure derived from the 2201-type has been synthesized for the first time. This oxide represents, like the homologous manganese phase, the n = 2 member of the large structural [Bi{sub 2}Sr{sub 2}MO{sub 6}]{sub n}[Sr{sub 8}M{sub 6}O{sub 16{+-}{delta}}] family (M = Cu, Co, Mn). Although its structure is similar to the Mn phase, it crystallizes in a different space group, Ammm (or Amm2), with a = 5.5232(2) {angstrom}, b = 23.465(1) {angstrom}, and c = 23.462(1) {angstrom}. The HREM study confirms that the structure consists of the stacking along b (or c) of 2201-type slices with single cobalt-deficient perovskite slices [Sr{sub 8}Co{sub 6}O{sub 6-{delta}}]. But the important difference with the Mn phase concerns the nature of the Co{sub 4} pillars, which are at the intersection of two [Sr{sub 8}Co{sub 6}O{sub 16{minus}{delta}}] slices. They form four corner-sharing CoO{sub 4} tetrahedra instead of MnO{sub 6} octahedra and MnO{sub 5} pyramids. This structural difference means that the Mn and Co phases do not form a complete solid solution. The tubular series Bi{sub 4{minus}y}Sr{sub 12{minus}z}Mn{sub 8{minus}x}Co{sub x}O{sub 28{+-}{delta}} could only be obtained for 0 {le} x {le} 2.5. The magnetic properties of this oxide are very complex and are very sensitive to the oxygen content. In particular, after oxygen pressure annealing, they are characteristic of spin-state transitions with temperature close to 50 and 450 K, similar to those observed in the LaCoO{sub 3} compound.
- OSTI ID:
- 323704
- Journal Information:
- Chemistry of Materials, Vol. 11, Issue 1; Other Information: PBD: Jan 1999
- Country of Publication:
- United States
- Language:
- English
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