New oxybromide cobaltites with layered perovskite-related structures: 18R-Ba6Co5BrO14 and 14H-Ba7Co6BrO17

Single crystals of the title compounds were prepared by solid–solid reaction using BaBr2 flux at 1373 K. The structures of these two new cobaltites were solved and refined. The two compounds are built from a close-packing of [BaO3] and [BaOBr] layers with stacking sequences (c′chhcc′)3 and (c′chhhcc′)2 for the 18R and 14H structures, respectively, which create Co3O12 trimers or Co4O15 tetramers of face-sharing octahedra connected at their extremities to isolated tetrahedra by corner-sharing. These new materials are strongly related to the 5H-Ba5Co5O14/12H-Ba0.9CoO2.6 and 10H-Ba5Co5ClO13/6H-Ba6Co6ClO16 materials, with the existence of common blocks. In Ba6Co5BrO14 and Ba7Co6BrO17, all the atoms in the vicinity of the [BaOBr] layers are disordered, whereas the rest of the structure is perfectly ordered.

[1]  O. Mentré,et al.  New BaCoO3-δ Polytypes by Rational Substitution of O2- for F- , 2007 .

[2]  O. Mentré,et al.  3D-magnetic ordering of Co4+ dimers in a new Co3+,4+ oxychloride: Neutron diffraction analysis and DFT calculations , 2006 .

[3]  A. Maignan,et al.  Large magnetoresistance in a ferromagnetic cobaltite: The 12H Ba0.9CoO2.6 , 2006 .

[4]  P. Roussel,et al.  Synthesis and structure of Ba6Co6ClO16, a new cobalt oxychloride with a layered perovskite-related structure , 2005 .

[5]  V. Caignaert,et al.  Thermoelectric power of HoBaCo2O5.5: possible evidence of the spin blockade in cobaltites. , 2004, Physical review letters.

[6]  Kazunori Takada,et al.  Superconductivity in two-dimensional CoO2 layers , 2003, Nature.

[7]  T. Welberry.  Diffuse X-ray scattering and strain effects in disordered crystals. , 2000, Acta crystallographica. Section A, Foundations of crystallography.

[8]  J. CavaR,et al.  交差連結鎖オキシ塩化コバルトBa 5 Co 5 ClO 13 の合成,結晶構造,及び磁気的と電気的な性質 , 2001 .

[9]  T. Proffen,et al.  DISCUS: a program for diffuse scattering and defect‐structure simulation , 1997 .

[10]  G. Sawatzky,et al.  Intermediate-spin state and properties of LaCoO3. , 1996, Physical review. B, Condensed matter.

[11]  A. Jacobson,et al.  An investigation of the structure of 12HBaCoO2.6 by electron microscopy and powder neutron diffraction , 1980 .

[12]  P. Coppens,et al.  Extinction within the limit of validity of the Darwin transfer equations. I. General formalism for primary and secondary extinction and their applications to spherical crystals , 1974 .

[13]  R. Ward,et al.  The Preparation of a Barium Cobalt Oxide and other Phases with Similar Structures1,2 , 1957 .

[14]  S. W. Strauss,et al.  Barium Cobalt Oxide of the Perowskite Type1,2 , 1951 .