The oxide Ba6Ga2Co11O26 : A new close-packed stacking derived from the hexagonal perovskite

Single crystals of a new compound, Ba 6 Ga 2 Co 11 O 26 , have been grown by a self-flux method. The structure determined by single-crystal X-ray diffraction and transmission electron microscopy (TEM) techniques shows a complex intergrowth between an hexagonal perovskite block, corresponding to the 5H term, and a complex block [Ba(Ga,Co) 8 O 11 ]. It crystallizes in the P3m1 trigonal space group with the following unit-cell parameters: a = 5.652(2)A b = 5.652(2) A, c = 18.828(8)A, and y = 120°. The structural analogy with two structural types, namely rocksalt and nolanite, allows a description of the nature of the [Ba(Ga,Co) 8 O 11 ] block: one central [111] RS Co 4 O 8 slab, related to a CdI 2 -type slice, is sandwiched between two Ba(Ga,Co) 2 O 3 nolanite-type slabs containing (Co/Ga)O 4 tetrahedra and (Co/Ga)O 6 octahedra. This compound can be thus viewed as the n = 5 member of the large series [Ba(Ga,Co) 8 O 11 ][BaCoO 3 ] n , opening the route toward the discovery of new cobaltites.