Formation of Co3+ octahedra and tetrahedra in YBaCo4O8.1

High-resolution neutron and synchrotron X-ray powder diffraction experiments were performed, at 300 and 10 K, for the determination of the structure of YBaCo4O8.1, which was prepared by controlled oxidation of the Kagomé lattice compound YBaCo4O7. Our diffraction data demonstrate that YBaCo4O8.1 crystallizes in the orthorhombic Pbc21 space group with the formation of a large superstructure (a=12.790 Å, b=10.845 Å, c=10.149 Å), with respect to the parent trigonal YBaCo4O7 material. The Co ions occupy both corner-sharing tetrahedral and edge-sharing octahedral sites, in contrast to YBaCo4O7, which has only corner-sharing tetrahedra. The octahedral sites form by the addition of two extra oxygen atoms and the drastic displacements of some of the original O atoms relative to the parent. The edge-sharing octahedra form isolated zigzag chains parallel to the c-axis linked to one another via tetrahedra. While found in a few phosphates, silicates and germanates, this motif appears unique to YBaCo4O8.1 among mixed-metal oxides. No structural phase transition or long range antiferromagnetic ordering are observed at 10 K.

Graphical abstractA new mixed-metal oxide of composition YBaCo4O8.1 has been synthesized by controlled oxidation of YBaCo4O7 and its structure determined using neutron and synchrotron X-ray powder diffraction. The structure features two alternating layers: a triangular layer of isolated CoO6 octahedra and CoO4 tetrahedra that links distorted Kagomé planes of charge-ordered Co ions. In these planes, a rarely observed motif of zigzag rows of edge-sharing octahedra is found, which are connected by ribbons of corner-sharing tetrahedra.Figure optionsDownload full-size imageDownload as PowerPoint slide